Lake Erie[5] (/ˈɪəri/) is the fourth-largest lake (by surface area) of the five Great Lakes in North America, and the eleventh-largest globally if measured in terms of surface area.[1][6] It is the southernmost, shallowest, and smallest by volume of the Great Lakes[7][8] and therefore also has the shortest average water residence time. At its deepest point Lake Erie is 210 feet (64 metres) deep.
Situated on the International Boundary between Canada and the United States, Lake Erie's northern shore is the Canadian province of Ontario, specifically the Ontario Peninsula, with the U.S. states of Michigan, Ohio, Pennsylvania, and New York on its western, southern, and eastern shores. These jurisdictions divide the surface area of the lake with water boundaries.
The lake was named by the Erie people, a Native American people who lived along its southern shore. The tribal name "erie" is a shortened form of the Iroquoian word erielhonan, meaning "long tail".[9]
Situated below Lake Huron, Erie's primary inlet is the Detroit River. The main natural outflow from the lake is via the Niagara River, which provides hydroelectric power to Canada and the U.S. as it spins huge turbines near Niagara Falls at Lewiston, New York and Queenston, Ontario.[10] Some outflow occurs via the Welland Canal, part of the St. Lawrence Seaway, which diverts water for ship passages from Port Colborne, Ontario on Lake Erie, to St. Catharines on Lake Ontario, an elevation difference of 326ft (99m). Lake Erie's environmental health has been an ongoing concern for decades, with issues such as overfishing, pollution, algae blooms, and eutrophication generating headlines.[11][12][13]
Geography

Geographic features

Lake Erie (42.2° N, 81.2W) has a mean elevation of 571 feet (174m)[3] above sea level. It has a surface area of 9,990 square miles (25,874km2)[2] with a length of 241 statute miles (388km; 209nmi)[2] and breadth of 57 statute miles (92km; 50nmi)[2] at its widest points.
It is the shallowest of the Great Lakes with an average depth of 10 fathoms 3 feet (63ft (19m)[2]  and a maximum depth of 35 fathoms (210ft; 64m)[2][3] For comparison, Lake Superior has an average depth of 80 fathoms 3 feet (483ft (147m), a volume of 2,900 cubic miles (12,000km3) and shoreline of 2,726 statute miles (4,385km). Because it is the shallowest, it is also the warmest of the Great Lakes,[14] and in 1999 this almost became a problem for two nuclear power plants which require cool lake water to keep their reactors cool.[15] The warm summer of 1999 caused lake temperatures to come close to the 85°F (29°C) limit necessary to keep the plants cool.[15] Also because of its shallowness, and in spite of being the warmest lake in the summer, it is also the first to freeze in the winter.[16] The shallowest section of Lake Erie is the western basin where depths average only 25 to 30 feet (7.6 to 9.1m); as a result, "the slightest breeze can kick up lively waves," according to a New York Times reporter in 2004.[17] The "waves build very quickly", according to other accounts.[18][19] Sometimes fierce waves springing up unexpectedly have led to dramatic rescues; in one instance, a Cleveland resident trying to measure the dock near his house became trapped but was rescued by a fire department diver from Avon Lake, Ohio:
In a tug of war against the waves, the two were finally hauled out by rope. After being trapped for an hour-and-a-half, Baker was back on dry land, exhausted and battered but alive.—Tatiana Morales, CBS News, 2004[20]

This area is also known as the "thunderstorm capital of Canada" with "breathtaking" lightning displays.[19] Lake Erie is primarily fed by the Detroit River (from Lake Huron and Lake St. Clair) and drains via the Niagara River and Niagara Falls into Lake Ontario. Navigation downstream is provided by the Welland Canal, part of the Saint Lawrence Seaway. Other major contributors to Lake Erie include the Grand River, the Huron River, the Maumee River, the Sandusky River, the Buffalo River, and the Cuyahoga River. The drainage basin covers 30,140 square miles (78,100km2).
Point Pelee National Park, the southernmost point of the Canadian mainland, is located on a peninsula extending into the lake. Several islands are found in the western end of the lake; these belong to Ohio except for Pelee Island and eight neighboring islands, which are part of Ontario.
Major cities along Lake Erie include Buffalo, New York; Erie, Pennsylvania; Toledo, Ohio; and Cleveland.

Islands

Islands tend to be located in the western side of the lake and total 31 in number (13 in Canada, 18 in the U.S.). The island-village of Put-in-Bay on South Bass Island attracts young crowds who sometimes wear "red bucket hats" and are prone to "break off cartwheels in the park" and general merriment.[21] Kelleys Island was depicted by the Chicago Tribune as having charms that were "more subtle" than Put-in-Bay, and offers amenities such as beach lounging, hiking, biking and "marveling at deep glacial grooves left in limestone."[21] Pelee Island is the largest of Erie's islands, accessible by ferry from Leamington, Ontario and Sandusky, Ohio. The island has a "fragile and unique ecosystem" with plants rarely found in Canada, such as wild hyacinth, yellow horse gentian (Triosteum angustifolium) and prickly pear cactus, as well as two endangered snakes, the blue racer and the Lake Erie water snake. Songbirds migrate to Pelee in spring, and monarch butterflies stop over during the fall.[22]
Water levels
Lake Erie has a lake retention time of 2.6 years,[23] the shortest of all the Great Lakes.[24] The lake's surface area is 9,910 square miles (25,667km2).[2][25] Lake Erie's water level fluctuates with the seasons as in the other Great Lakes. Generally, the lowest levels are in January and February, and the highest in June or July, although there have been exceptions. The average yearly level varies depending on long-term precipitation. Short-term level changes are often caused by seiches that are particularly high when southwesterly winds blow across the length of the lake during storms. These cause water to pile up at the eastern end of the lake. Storm-driven seiches can cause damage onshore. During one storm in November 2003, the water level at Buffalo rose by 7 feet (2.1m) with waves of 10–15 feet (3.0–4.6 metres) for a rise of 22 feet (6.7m).[26] Meanwhile, at the western end of the lake, Toledo experienced a similar drop in water level. Lake water is used for drinking purposes.[27]
Historic High Water. The lake fluctuates from month to month with the highest lake levels in June and July. In the summer of 1986, Lake Erie reached its highest level at 5.08 feet (1.55m) above datum.[28]  The high water records were set from 1986 (April) through January 1987. Levels ranged from 4.33to 5.08 feet (1.32–1.55m) above Chart Datum.[28]
Historic Low Water. Lake Erie experiences its lowest levels in the winter. In the winter of 1934, Lake Erie reached its lowest level at 1.5 feet (0.46m) below datum.[28] Monthly low water records were set from July 1934 through June 1935. During this twelve-month period water levels ranged from 1.5 feet (0.46m) to the Chart Datum.[28]
Geology

Lake Erie was carved out by glacier ice,[1] and in its current form is less than 4,000 years old, which is a short span in geological terms. Before this, the land on which the lake now sits went through several complex stages. A large lowland basin formed over two million years ago as a result of an eastern flowing river that existed well before the Pleistocene ice ages. This ancient drainage system was destroyed by the first major glacier in the area, while it deepened and enlarged the lowland areas, allowing water to settle and form a lake. The glaciers were able to carve away more land on the eastern side of the lowland because the bedrock is made of shale which is softer than the carbonate rocks of dolomite and limestone on the western side. Thus, the eastern and central basins of the modern lake are much deeper than the western basin, which averages only 25 feet (7.6m) deep and is rich in nutrients and fish.[34] Lake Erie is the shallowest of the Great Lakes because the ice was relatively thin and lacked erosion power when it reached that far south, according to one view.
As many as three glaciers advanced and retreated over the land causing temporary lakes to form in the time periods in between each of them. Because each lake had a different volume of water their shorelines rested at differing elevations. The last of these lakes to form, Lake Warren, existed between about 13,000 and 12,000 years ago. It was deeper than the current Lake Erie, so its shoreline existed about eight miles (13km) inland from the modern one. The shorelines of these lakes left behind high ground sand ridges that cut through swamps and were used as trails for Indians and later, pioneers. These trails became primitive roads which were eventually paved. U.S. Route 30 west of Delphos and U.S. Route 20 west of Norwalk and east of Cleveland were formed in this manner. One can still see some of these ancient sand dunes that formed in the Oak Openings Region in Northwestern Ohio. There, the sandy dry lake bed soil was not enough to support large trees with the exception of a few species of oaks, forming a rare oak savanna.[35]
History
Native Americans
At the time of European contact, there were several groups of Native American cultures living around the shores of the eastern end of the lake. The Erie tribe (from whom the lake takes its name) lived along the southern edge, while the Neutrals (also known as Attawandaron) lived along the northern shore. Near Port Stanley, there is a Native American village dating from the 16th century known as the Southwold Earthworks where as many as 800 Neutral Native Americans once lived; the archaeological remains include double earth walls winding around the grass-covered perimeter.[22] Europeans named the tribe the Neutral Indians since these people refused to fight with other tribes.[22] Both tribes were conquered and assimilated by their hostile eastern neighbors, the Iroquois Confederacy between AD 1651 and 1657, in what is referred to as part of the Beaver Wars.[36]
For decades after those wars, the land around eastern Lake Erie was claimed and utilized by the Iroquois as a hunting ground. As the power of the Iroquois waned during the last quarter of the 17th century, several other, mainly Anishinaabe Native American tribes, displaced them from the territories they claimed on the north shore of the lake.[37] There was a legend of a Native American woman named Huldah, who, despairing over her lost British lover, hurled herself from a high rock from Pelee Island.[18]
European exploration and settlement

In 1669, the Frenchman Louis Jolliet was the first documented European to sight Lake Erie, although there is speculation that Étienne Brûlé may have come across it in 1615.[38] Lake Erie was the last of the Great Lakes to be explored by Europeans, since the Iroquois who occupied the Niagara River area were in conflict with the French, and they did not allow explorers or traders to pass through. Explorers followed rivers out of Lake Ontario and portaged directly into Lake Huron. British authorities in Canada were nervous about possible expansion by American settlers across Lake Erie, so Colonel Talbot developed the Talbot Trail in 1809 as a way to stimulate settlement to the area; Talbot recruited settlers from Ireland and Scotland and there are numerous places named after him, such as Port Talbot and the Talbot River and Talbotville in southern Ontario.[22]

During the War of 1812, Oliver Hazard Perry captured an entire British fleet in 1813[39] near Put-in-Bay, Ohio, despite having inferior numbers.[40] American soldiers swept through the Ontario area around Port Rowan burning towns and villages, but spared a gristmill owned by a Canadian mason named John Backhouse, according to one report.[22] Generally, however, despite the two exceptions being the American Revolutionary War and the War of 1812 which involved conflicts between the U.S. and Great Britain, relations between the U.S. and Canada have been remarkably friendly with an "unfortified boundary" and an agreement "that has kept all fleets of war off the Great Lakes."[41]
In 1837, rebellions broke about between Canadian settlers and the British Colonial government. These primarily concerned political reforms and land allocation issues. Some of the rebels stationed themselves in the U.S. and crossed the ice from Sandusky Bay to Pelee Island wearing "tattered overcoats and worn-out boots", and carrying muskets, pitchforks, and swords,[18] but the islanders had already fled.[18] Later, there was a battle on the ice with the Royal 32nd regiment, with the rebels being driven to retreat.[18]

Settlers established commercial fisheries on the north coast of the lake around the 1850s.[42] An important business was fishing.[23] In the pre-Civil War years, railways sprouted everywhere, and around 1852 there were railways circling the lake.[43] Maritime traffic picked up, although the lake was usually closed because of ice from December to early April, and ships had to wait for the ice to clear before proceeding.[44] Since slavery had been abolished in Canada in 1833, but was still legal in southern states of the U.S., a Lake Erie crossing was sometimes required for fugitive slaves seeking freedom:
When Kentucky fugitive Lewis Clarke arrived in Cleveland, he had no idea how to find Canada. "I went out to the shore of the lake again and again, to try and see the other side, but I could see no hill, mountain, nor city of the asylum I sought," he once told an interviewer. "I was afraid to inquire where (Canada) was, lest it would betray such a degree of ignorance as to excite suspicion at once." Many fugitives also had to overcome fears instilled by their former masters ...—Chris Lackner in the Ottawa Citizen, 2006[45]

Merchant shippers lacked modern radar and weather forecasting so vessels were often caught up in intense gales:
A violent gale is blowing on Lake Erie ... The schooner Stranger came in this morning and reports seeing a vessel about 12 miles [19km] up, 2 miles [3.2km] from the Canada shore, with three men clinging to the masts, which alone were visible above the water–heard their cries and screams ...—The New York Times, October 1853[46]

There were reports of disasters usually from sea captains passing information to reporters; in 1868, the captain of the Grace Whitney saw a sunken vessel "three men clinging to the masthead" but he could not help because of the gale and high seas.[47]
A balloonist named John Steiner of Philadelphia made an ambitious trip across the lake in 1857.[48] He was described in The New York Times as an eronaut or aeronaut; powered boats were called propellers; and fast was deemed railroad speed. Here's an account of the day-long voyage over the lake:
He arose to the height of about three miles, and started off at a slow but steady rate ... The lake could be seen from one end to the other nearly ... At one time Mr. Steiner counted 38 sail vessels, all in sight, and far below him. The hands on board several of the vessels saw him, and rightly apprehending that he was an aeronaut, cheered him heartily ... He neared the Canada shore a little below Long Point ... he was accordingly driven towards Buffalo ... Night was drawing on and it became apparent that he could not, with this current, get away from the water before dark, and after nightfall it would not be safe to come down. Seeing a propeller ... the Mary Stewart ... He first struck the water about 25 miles below Long Point ... During this time Mr. Steiner says he thinks his balloon bounded from the water at least twenty times. It would strike and then rebound, like a ball, going into the air from twenty to fifty feet, and still rushing down the lake at railroad speed ... Mr. Steiner then abandoned the balloon, leaping into the water and swimming towards the boat, which speedily reached him ...—The New York Times, July 23, 1857[48]

In 1885, lake winds were so strong that water levels dropped substantially, sometimes by as much as two feet, so that at ports such as Toledo, watercraft could not load coal or depart the port.[49]
During the history of the lake as a fishery, there has been marked battling by opposing interest groups. Here's an 1895 newspaper account in which critics of commercial fishing issued dire predictions and calling for government action to solve the problem:
The preservation of the fisheries of Lake Erie has become a serious problem to all who have given it close attention ... the fisheries are being exhausted by the wasteful methods which are now in vogue ... it is still the custom of the pound fishermen about Sandusky to take fish of all sizes, and if they are too small to be marketable they are turned over to a fertilizer factory. If left undisturbed for two or three years more, these little fish would be a very valuable product ...—The New York Times, 1895[50]

Predictions of the lake being over-fished in 1895 were premature, since the fishery has survived commercial and sport fishing, pollution in the middle of the 20th century, invasive species and other ailments, but state and provincial governments, as well as national governments, have played a greater role as time went by. Business boomed; in 1901, the Carnegie Company proposed building a new harbor near Erie in Elk Creek to accommodate shipments from its tube-plant site nearby.[51] In 1913, a memorial to Commodore Perry was built on Put-in-Bay island featuring a Doric column.[41]
During the Prohibition years from 1919 to 1933, a "great deal of alcohol crossed Erie"[18] along with "mobster corpses" dumped into the Detroit River which sometimes washed up on the beaches of Pelee Island.[52] According to one account, Al Capone hid a "fortune" in the walls of the Middle Island luxury club, but no money was found in it as of 2007 when the building no longer stood.[18] The club had a basement casino with poker tables and slot machines.[18]
During the 20th century, commercial fishing was prevalent, but so was the boom in manufacturing industry around the lake, and often rivers and streams were used as sewers to flush untreated sewage which ended up in the lake.[53] Sometimes poorly constructed sanitary systems meant that when old mains broke, raw sewage would spill directly into the Cuyahoga and into the lake.[53] A report in Time magazine in 1969 described the lake as a "gigantic cesspool" since only three of 62 beaches were rated "completely safe for swimming".[53]
By 1975 the popular commercial fish blue pike had been declared extinct, although the declaration may have been premature.[54] By the 1980s, there were about 130 fishing vessels with about 3,000 workers,[42] but commercial fishing was declining rapidly, particularly from the American side.
Great Lakes Compact

In 2005, the Great Lakes States of Ohio, Michigan, New York, Pennsylvania, Illinois, Indiana, Wisconsin, Minnesota and the Canadian Provinces of Ontario and Quebec endorsed the Great Lakes-St. Lawrence River Basin Sustainable Water Resources Compact (Compact). The Compact was signed into law by President George W. Bush in September 2008. An international water rights policy overseen by the Great Lakes Commission, the Compact aims to prevent diversion of water from Great Lakes to distant states, as well as to set standards for use and conservation. It had support from both political parties, including former United States Senator George Voinovich (R-OH) and former Governor Jennifer Granholm (D-MI), but is not popular in the southwestern states due to frequent drought conditions and water scarcity.
Lake environment
Climate
Lake Erie in winter

Like the other Great Lakes, Erie produces lake effect snow when the first cold winds of winter pass over the warm waters. When the difference in temperature between the relatively warm surface water and the colder air reaches a threshold value of 18 to 23 degrees Fahrenheit (-5 to -8 degrees Celsius), then "lake-effect snow becomes possible:"[55]
As cold air flows over the warm water, the lake warms and moistens the air. Since warm, moist air is less dense than cold air, the heated air rises. Rising air cools and water vapor condenses into cloud droplets ... the efficiency of snow production increases when the wind pushes the clouds over land. Friction with the ground causes air to pile up. This frictional convergence creates lift and enhances snowfall.—Bob Swanson and Adrienne Lewis of USA Today, 2008[55]

Heavy lake-effect snowfalls can occur when cold air travels 60 miles (97km) or longer over a large unfrozen lake.[55] Lake-effect snow makes Buffalo and Erie the eleventh and thirteenth snowiest places in the entire United States respectively, according to data collected from the National Climatic Data Center.[56] Since winds blow primarily west–to–east along the main axis of the lake, lake effect snow effects are more pronounced on the eastern parts of the lake such as cities such as Buffalo and Erie. Buffalo typically gets 95 inches (240cm) of snow each winter, and sometimes ten feet (3.0m) of snow;[57] the snowiest city is Syracuse, New York, which can receive heavy snowfall from both the lake effect process and large coastal cyclones. A storm around Christmas in 2001 pounded Buffalo with seven feet of snow.[58]

The lake effect ends or its effect is reduced, however, when the lake freezes over. In January 2011, for example, residents of Cleveland were glad when Lake Erie was "90 percent frozen" since it meant that the area had "made it over the hump" in terms of enduring repeated snowfalls which required much shoveling.[59] Being the shallowest of the Great Lakes, it is the most likely to freeze and frequently does.[60] On February 16, 2010, meteorologists reported that the lake had frozen over marking the first time the lake had completely frozen over since the winter of 1995–1996.[61] In contrast, Lake Michigan has never completely frozen over since the warmer and deeper portion is in the south, although it came close to being totally frozen during three harsh winters over the past century.[62] When the lake freezes over, this usually shuts down the lake effect snowfall.[63] In past years, lake ice was so thick that it was possible to drive over it or go sailing on iceboats; but in the first decade of the 21st century, the ice has not been thick enough for such activities.[52] Many lake residents take advantage of the ice and travel; some drive to Canada and back.[64] Here's one account of ice life around Put-in-Bay:
The first ice usually forms in late November, and by January it locks into place. For islanders in the Western Basin, it is the equivalent of summer vacation ... Once the lake freezes, islanders organize impromptu ice rallies. Families gather to drink hot wine and race all-terrain vehicles across the lake. They also race iceboats, which resemble sailboats on skates ... Many people drive to other islands for dinner with friends. They ride in cars with the roofs and doors chopped off so they can escape if the vehicles fall through the ice. Islanders stab evergreen trees into the ice every 50 yards to mark a route ... Even in the coldest winters, there are dangerous patches of thin ice. The cracks are so predictable that the Put-in-Bay Ice Yacht Club prints them on a map ... On a normal winter day, the ice is dotted with 2,000 fishing shanties.—Christopher Maag in The New York Times, 2004[64]

Windy conditions
Strong winds have caused lake currents to shift sediment on the bottom, leading to "wickedly shifting sandbars" that have been the cause of shipwrecks.[52] But winds can have a peaceful purpose as well; there have been proposals to place electricity–producing wind turbines in windy and shallow points in the lake and along the coast, both in the United States and Canada. In 2010, there were plans for GE to develop five wind turbines to generate 20 megawatts of power by 2012 with plans to generate 1,000 megawatts by 2020; one proposal called for "gearless turbines" with 176-foot long blades helped along with magnets.[65][66] A nonprofit development group near Cleveland was developing plans to construct hundreds of turbines in the lake.[67]  A former steel mill site on the eastern edge of the lake in Buffalo, NY has been redeveloped as an urban wind farm in 2007. Known as Steel Winds, the project currently houses 14 turbines capable of generating up to 35 megawatts of electricity.[68]  A plan by Samsung to build an offshore wind farm on the north shore of the lake, from Port Maitland to Nanticoke for a distance of 15.5mi (24.9km),[69] but the plan has been met with opposition from residents for a number of reasons. Canadians near Leamington and Kingsville have organized protest groups to thwart attempts to bring wind turbines to the lake; reasons against the turbines include spoiling lake views as well as possible adverse effects regarding drinking water and commercial fishing.[70] Plans to install turbines in Pigeon Bay, south of Leamington were met with opposition as well.[71][72] The notion that bird and bat migration may be hurt by the wind turbines has been used to argue against the wind turbines; a reporter in The Globe and Mail wrote "Given the tendency of turbines to make mincemeat of things airborne, it doesn't require great imagination to figure out what would happen."[70]
They loom like gigantic aliens invading the farmers' fields. There are 66 of these creatures, each about as tall as a 25-storey building with a face comprised of three enormous whiskers rotating 11 to 20 times per minute. Standing amidst the wind turbines of Erie Shore Wind Farm, one feels like a doomed character in a sci-fi movie caught in the deathly still moment just before disaster strikes.—reporter Rebecca Field Jager in the Weekend Post, 2010[73]

Microclimates
The lake is also responsible for microclimates that are important to agriculture. Along its north shore is one of the richest areas of Canada's fruit and vegetable production; this southernmost tip, particularly in the area around Leamington, is known as Canada's "tomato capital".[70] The area around Port Rowan in Ontario has special trees which grow because of the "tempering effect of the lake", and species include tulip trees, flowering dogwood, sassafras and sour gum.[22] In this area there are many greenhouses which produce a "variety of tropical plants rarely cultivated so far north", including some species of cacti, because of the lake's tempering effect.[22] Along the southeastern shore of Ohio, Pennsylvania, and New York is an important grape growing region, as are the islands in the lake. Apple orchards are abundant in northeast Ohio to western New York.
Long term weather patterns
According to one estimate, 34 to 36 inches of water evaporates each year from the surface of the lake,[1] which allows for rainfall and other precipitation in surrounding areas. There are conflicting reports about the overall effect of global warming on the Great Lakes region, including Lake Erie. One account suggests that climate change is causing greater evaporation of lake water, leading to warmer temperatures as well as ice in winter which is less thick or nonexistent, fueling concerns that "Erie appears to be shrinking" and is the most likely candidate among the five Great Lakes to "turn into a festering mud puddle."[52] In 2010, the Windsor Star reported that the lake experienced "record-breaking temperatures" reaching 81°F (27°C) in mid-August and compared the lake to a "bath tub".[74] But the long term weather patterns are subject to controversy.
Ecosystems

Lake Erie has a complex ecosystem with many species in constant interaction. Human activity, such as pollution and maritime ship traffic, can affect this environment in numerous ways. The interactions between the new species can sometimes have beneficial effects, as well as harmful effects. Some introductions have been seen as beneficial such as the introduction of Pacific salmon.[52] Occasionally there have been mass die-offs of certain species of fish, sometimes for reasons unknown, such as many numbers of rainbow smelt in May 2010.[75]
Invasive species
The lake has been plagued with a number of invasive species, including zebra[52] and quagga mussels, the goby and the grass carp. One estimate was that there have been 180 invasive species in the Great Lakes, some having traveled in ballast water in international ships.[76] Zebra mussels and gobies have been credited with the increased population and size of smallmouth bass in Lake Erie.[77] In 2008 there were concerns that the "newest invader swarming in the Great Lakes", which was the "bloody-red shrimp", might harm fish populations and promote algae blooms.[78]
Environmentalists and biologists study lake conditions via installations such as the Franz Theodore Stone Laboratory on Gibraltar Island. The lab, which was established in 1895, is the oldest biological field station in the United States. Stone Laboratory was donated to the Ohio State University by Julius Stone in 1925 as part of the university's Ohio Sea Grant College Program.[34][76] In addition, the Great Lakes Institute of the University of Windsor has experts who study issues such as lake sediment pollution and the flow of contaminants such as phosphorus.[76]
A list of the common invasive species in Lake Erie include: Zebra Mussels, Quagga Mussels, Round Gobies, Spiny European Water Fleas, Fishhook Water Fleas, the Sea Lamprey, and White Perch. The invasive plant species that fill Lake Erie consist mainly of Eurasian Milfoil, and Purple Loosestrife,
Eutrophication and the infamous dead zone

An ongoing concern is that "nutrient overloading from fertilizers, human and animal waste", known as eutrophication, in which additional nitrogen and phosphorus enter the lake, will cause plant life to "run wild and multiply like crazy".[11] Since there are fewer wetlands, which are like "Nature's kidneys" by filtering nutrients, as well as greater "channelization of waterways", nutrients in water can cause algal blooms to sprout as well as "low-oxygen dead zones" in a complex interaction of natural forces.[11] As of the 2010s much of the phosphorus in the lake comes from fertilizer applied to no-till soybean and corn fields but washed into streams by heavy rains. The algal blooms result from growth of Microcystis, a toxic blue-green algae that the zebra mussels which infest the lake don't eat.[12]
There periodically is a dead zone, or region of low oxygen, in the lake whose exact location varies. Scientists from the National Oceanic and Atmospheric Administration have been studying the lake's blue-green algae blooms, and trying to find ways to predict when they are spreading or where they might hit landfall; typically the blooms arrive late each summer.[13] This problem was extreme in the mid and late 1960s and the Lake Erie Wastewater Management Study (LEWMS) conducted by the Buffalo District of the US Army Corps of Engineers determined that the eutrophication was due to "point sources" such as industrial outfalls and municipal sanitary and storm sewer outfalls, as well as "diffuse sources", such as overland runoff from farm and forest land. All these sources contribute nutrients, primarily phosphorus, to the lake. Growth of organisms in the lake is then spiked to the point that oxygen levels are depleted. LEWMS made recommendations for reducing point source outflows, as well as reducing farm contributions of phosphorus by changing fertilizer usage, employing "no-till" farming and other conservative practices. Many industrial and municipal sources have since then been greatly reduced. The improved farming practices, which were voluntary, were followed for a while, resulting in remarkable recovery of the lake in the 1970s.[79]
Unfortunately, the conservative practices are not monitored and have not been kept up. One recent account suggests that the seasonal algae blooms in Lake Erie were possibly caused by "runoff from cities, fertilizers, zebra mussels, and livestock near water."[13] A second report focuses on the zebra mussels as being the cause of "big oxygen-poor dead zones" since they filter so much sediment that this produces an overgrowth of algae.[52] One report suggests the oxygen-poor zone began about 1993 in the lake's central basin and becomes more pronounced during summer months, but it is somewhat of a mystery why this happens.[80] Some scientists speculate that the dead zone is a naturally occurring phenomenon.[76] Another report cited Ohio's Maumee River as the main source of polluted runoff of phosphorus from industries, municipalities, tributaries and agriculture, and in 2008, satellite images showed the algal bloom heading toward Pelee Island, and possibly heading to Lake Erie's central basin.[76] There have been two-year $2 million studies trying to understand the "growing zone" which was described as a "10-foot-thick layer of cold water at the bottom", 55 feet (17m) in one area, which stretches "100 miles across the lake's center".[80] It kills fish and microscopic creatures of the lake's food chain and fouls the water, and may cause further problems in later years for sport and commercial fishing.[80]
Algae blooms continued in early 2013 but new farming techniques, climate change and even a change in Lake Erie's ecosystem make phosphorus pollution more intractable.[81]
Snakes

The Lake Erie water snake, a subspecies of the northern water snake (Nerodia sipedon), lives in the vicinity of Ohio's Put-in-Bay Harbor, and had been put on the threatened species list.[82] A threatened species is one which may soon become an endangered species.[83] By 2010, the water snake population was over 12,000 snakes.[82] While they have a non-venomous bite, they are a key predator in the lake's aquatic ecosystem since they feed on mudpuppies and walleye and smallmouth bass.[82] The snake was helpful in keeping the population of goby fish in check.[82] They mate from late May through early June and can be found in large mating balls with one female bunched with several males.[83]
Asian carp
There is a concern that Asian carp might enter the Great Lakes region and alter the ecosystem negatively.[42] They have been described as "greedy giants that suck plankton from the water with the brutal efficiency of vacuum cleaners" and scientists worry that they may unravel the "aquatic food web" by crowding out other species.[42]
Snakehead fish

There was concern in 2007 that snakehead fish could get into the Great Lakes area.[84] Officials warn that if the fish invades, it could "decimate the aquatic food chain".[84] A YouTube video mentioned in a newspaper account has a man claiming that the fish could "bite your entire hand off". The fish can reach 5feet 11inches (1.80m) in length and "survive out of water for four days" and "has a mouth full of teeth that can shear fish in half" and can "eat ducks and small mammals."[84] The snakehead fish can not live in a lake that has completely frozen over. They must come to the surface to breathe via their swim bladder.
It gets such huge sizes. It moves over land and it breathes air and it will eat anything it comes into contact with. That's what freaks people out about it, to see a fish moving across land gulping air.—about the Snakehead fish, 2007, CanWest News Service[84]

Agriculture and life around the lake
In 1999, Doppler radar weather sensors detected millions of mayflies heading for Presque Isle in blue and green splotches on the radar in clouds measuring ten miles (16km) long.[85] These insects were a sign of Lake Erie's move back to health, since the mayflies require clean water to thrive.[85] Biologist Masteller of Penn State Erie declared the bugs to be a "nice nuisance" since they signified the lake's return to health after forty years of absence.[85] Each is an inch and a half long; the three main species of mayflies are Ephemera simulans, Hexagenia rigida and Hexagenia limbata.[85] The insects mate over a 72-hour period from June through September; they fly in masses up to the shore, mate in the air, then females lay up to 8,000 eggs each over the water; the eggs sink back down and the cycle repeats.[85] Sometimes the clouds of mayflies have caused power outages[86] as well as causing roads to become slippery with squashed insects.[85] Since zebra mussels filter extra nutrients from the lake, it allows the mayfly larvae to thrive.[86]

There have been incidents of birds dying from botulism, in 2000,[87] and in 2002.[88] Birds affected included grebes, common and red-breasted mergansers, loons, diving ducks, ring-billed gulls and herring gulls.[87] One account suggests that bird populations are in trouble, notably the woodland warbler, which had population declines around 60 percent in 2008.[52] Possible causes for declines in bird populations are farming practices, loss of habitats, soil depletion and erosion, and toxic chemicals.[52] In 2006, there were concerns of possible bird flu after two wild swans on the lake were found diseased, but it was learned that they did not contain the deadly H5N1 virus.[89] There were sightings of a magnificent frigatebird, a tropical bird with a two-metre wingspan, over the lake in 2008.[90]
Water quality issues and restoration
Lake Erie infamously became very polluted in the 1960s and 1970s as a result of the quantity of heavy industry situated in cities on its shores, with reports of bacteria-laden beaches and fish contaminated by industrial waste.[91] In the 1970s, patches of the lake were declared dead because of industrial waste as well as sewage from runoffs; as The New York Times reporter Denny Lee wrote in 2004, "The lake, after all, is where the Rust Belt meets the water."[17]
The water quality deteriorated partially due to increasing levels of the nutrient phosphorus[76] in both the water and lake bottom sediments. The resultant high nitrogen levels in the water caused eutrophication, which resulted in algal blooms and algae masses[92] and fish kills increasingly fouled the shoreline during this period. There were incidents of the oily surfaces of tributary rivers emptying into Lake Erie catching fire: in 1969, Cleveland's Cuyahoga River erupted in flames,[92] chronicled in a Time magazine article which lamented a tendency to use rivers flowing through major cities as "convenient, free sewers";[53] the Detroit River caught fire on another occasion.[52] The outlook was gloomy:
Each day, Detroit, Cleveland and 120 other municipalities fill Erie with 1.5 billion gallons of "inadequately treated wastes, including nitrates and phosphates ... These chemicals act as fertilizer for growths of algae that suck oxygen from the lower depths and rise to the surface as odoriferous green scum ... Commercial and game fish—blue pike, whitefish, sturgeon, northern pike—have nearly vanished, yielding the waters to trash fish that need less oxygen. Weeds proliferate, turning water frontage into swamp. In short, Lake Erie is in danger of dying by suffocation.—Time magazine, August 1969[53]

These events embarrassed officials and spurred local officials, including Cleveland's director of public utilities, Ben Stefanski, to pursue a massive effort to "scrub the Cuyahoga"; the effort cost $100 million in bonds, according to one estimate.[53] New sewer lines were built.[53] Clevelanders approved a bond issue by 2 to 1 to seriously upgrade Cleveland's sewage system.[53] Federal officials acted as well; the United States Congress passed the Clean Water Act of 1972.[92][93] In that year, the United States and Canada established water pollution limits in an International Water Quality Agreement. The Corps' LEWMS, mentioned above, was also instituted at that time. The controls were effective, but it took several decades to take effect; by 1999, there were signs that large numbers of mayflies were spotted on the lake after a forty-year absence, signalling a return to health.[17][85]
The clearing of the water column is also partly due to the introduction and rapid spread of zebra mussels from Europe, which had the effect of covering "the basin floor like shag carpeting" with each creature filtering "a liter of fresh water a day," helping to restore the lake to a cleaner state.[17] The 1972 Great Lakes Water Quality Agreement also significantly reduced the dumping and runoff of phosphorus into the lake. The lake has since become clean enough to allow sunlight to infiltrate its water and produce algae and sea weed, but a dead zone persists in the central Lake Erie Basin during the late summer. The United States Environmental Protection Agency has studied this cyclic phenomenon since 2005.[94] There have been instances of beach closings at Presque Isle off the coast of northwestern Pennsylvania because of unexplained E. Coli contaminations,[95] possibly caused by storm water overflows after heavy downpours.

Since the 1970s environmental regulation has led to a great increase in water quality and the return of economically important fish species such as walleye and other biological life.[96] There was substantial evidence that the new controls had substantially reduced levels of DDT in the water by 1979.[27] Cleanup efforts were described in 1979 as a notable environmental success story, suggesting that the cumulative effect of legislation, studies, and bans had reversed the effects of pollution:[27]
The globs of oil, the multicolored industrial discharges, the flotsam from shoreline cities, the fecal and bacterial wastes are no longer dumped in the lakes in vast quantities.—Time magazine, 1979[27]

Joint U.S.–Canadian agreements pushed 600 of 864 major industrial dischargers to meet requirements for keeping the water clean.[27] One estimate was that $5billion was spent to upgrade plants to treat sewage.[27] The change toward cleaner water has been in a positive direction since the 1970s.
Other ecosystem related issues
There was a tentative exploratory plan to capture CO2, compress it to a liquid form, and pump it a half-mile (800 m) beneath Lake Erie's surface underneath the porous rock structure.[97] According to chemical engineer Peter Douglas, there is sufficient storage space beneath Lake Erie to hold between 15 and 50 years of liquid CO2 emissions from the 4,000 megawatt Nanticoke coal plant.[97] But there has been no substantial progress on this issue since 2007.
Economy
Fishing
Species of fish

Lake Erie is home to one of the world's largest freshwater commercial fisheries. Lake Erie's fish populations are the most abundant of the Great Lakes, partially because of the lake's relatively mild temperatures and plentiful supply of plankton, which is the basic building block of the food chain.[42] The lake's fish population accounts for an estimated 50% of all fish inhabiting the Great Lakes.[98] The lake is "loaded with superstars" such as steelhead,[99] walleye (American usage) or pickerel (Canadian usage),[42][99] smallmouth bass,[99] perch,[99] as well as bass, trout, salmon, whitefesh, smelt, and many others.[42] The lake consists of a long list of well established introduced species. Common non-indigenous fish species include the rainbow smelt, alewife, white perch and common carp. Non-native sport fish such as rainbow trout and brown trout are stocked specifically for anglers to catch. Attempts failed to stock coho salmon and its numbers are once again dwindling. Commercial landings are dominated by yellow perch and walleye, with substantial quantities of rainbow smelt and white bass also taken. Anglers target walleye and yellow perch, with some effort directed at rainbow trout. A variety of other species are taken in smaller quantities by both commercial and sport fleets.
Up until the end of the 1950s, the most commonly caught commercial fish (more than 50% of the commercial catch) was a subspecies of the walleye known as the blue walleye (Sander vitreus glaucus) sometimes erroneously called "blue pike". In the 1970s and 1980s, as pollution in the lake declined, counts of walleyes which were caught grew from 112,000 in 1975 to 4.1 million in 1985, with estimates of the numbers of walleyes in the lake at around 33 million in the basin, with many of 8 pounds or more.[100] Not all walleyes thrived. The combination of overfishing and the eutrophication of the lake by pollution caused the population to collapse, and in the mid-1980s, one species of walleye called the blue walleye was declared extinct. But the Lake Erie walleye was reportedly having record numbers, even in 1989, according to one report.[101] There have been concerns about rising levels of mercury in walleye fish; a study by the Canadian Ministry of the Environment noted an "increasing concentration trend" but that limits were within acceptable established by authorities in Pennsylvania.[102] It was recommended, because of PCBs, that persons eat no more than one walleye meal per month.[102] Because of these and other concerns, in 1990, the National Wildlife Federation was on the verge of having a "negative fish consumption advisory" for walleyes and smallmouth bass, which had been the bread-and-butter catch of an $800 million commercial fishing industry.[103]
The longest fish in Lake Erie is reportedly the sturgeon which can grow to ten feet long and weight 300 pounds, but it is an endangered species and mostly lives on the bottom of the lake.[104] In 2009, there was a confirmed instance of a sturgeon being caught, which was returned to the lake alive, and there are hopes that the population of sturgeons is resurging.[105]
Commercial fishing

Estimates vary about the fishing market for the Great Lakes region. One estimate of the total market for fishing, including commercial as well as sport or recreational fishing, for all of the Great Lakes, was $4 billion annually, in 2007.[13] A second estimate was that the fishing industry was valued at more than $7 billion.[42]
But since high levels of pollution were discovered in the 1960s and 1970s, there has been continued debate over the desired intensity of commercial fishing. Commercial fishing in Lake Erie has been hurt by the bad economy as well as government regulations which limit the size of their catch; one report suggested that the numbers of fishing boats and employees had declined by two-thirds in recent decades.[42] Another concern had been that pollution in the lake, as well as toxins found inside fish, were working against commercial fishing interests.[92] U.S. fishermen based along Lake Erie "lost their livelihood" over the past few decades described as being "caught in a net of laws and bans", according to the Pittsburgh Post-Gazette, and no longer catch fish such as whitefish for markets in New York.[23] Pennsylvania had a special $3 stamp on fishing licenses to help "compensate commercial fishermen for their losses", but this program ended after five years turning Erie's commercial fishing industry into an "artifact."[23] One blamed the commercial fishing ban after a "test of wills" between commercial and recreational fishermen: "One side needed large hauls. The other feared the lake was being emptied."[23]
Commercial fishing is now predominantly based in Canadian communities, with a much smaller fishery—largely restricted to yellow perch—in Ohio. One account suggested that Canadian fishermen are "still at it and making money" and they "know how to fish" by "using the old nets."[23] The Ontario fishery is one of the most intensively managed in the world. However, there are reports that some Canadian commercial fishermen are dissatisfied with fishing quotas, and have sued their government about this matter, and there have been complaints that the legislative body writing the quotas is "dominated by the U.S." and that sport fishing interests are favored at the expense of commercial fishing interests.[106] Cuts of 30 to 45 percent for certain fish were made in 2007.[106] The Lake Erie fishery was one of the first fisheries in the world managed on individual transferable quotas and features mandatory daily catch reporting and intensive auditing of the catch reporting system. Still, the commercial fishery is the target of critics who would like to see the lake managed for the exclusive benefit of sport fishing and the various industries serving the sport fishery. In November 2010, Ontario's oldest and largest fish processor known as Great Lakes Fish Corporation was shut down after operating for a hundred years; 130 workers were laid off and numerous spinoff jobs disappeared, such as jobs at local restaurants and net repair shops.[107] According to one report, the Canadian town of Port Dover is the home of the lake's largest fishing fleet, and the town features miniature golf, dairy bars, French-fry stands, and restaurants serving perch.[22]
Government regulation of fishing
The lake can be thought of as a common asset with multiple purposes including being a fishery. There was direct competition between commercial fishermen and sport fishermen (including charter boats and sales of fishing licenses) throughout the lake's history, with both sides seeking government assistance from either Washington or Ottawa, and trying to make their case in the "court" of public opinion through newspaper reporting.[50] But other groups have entered the political process as well, including environmentalists, lakefront property owners, industry owners and workers seeking cost-effective solutions for sewage, ferry boat operators, even corporations making electric-generating wind turbines.
Management of the fishery is by consensus of all management agencies with an interest in the resource and include the states of New York, Pennsylvania, Ohio, Michigan and the province of Ontario, and work under the mandate of the Great Lakes Fishery Commission. The commission makes assessments using sophisticated mathematical modeling systems. The Commission has been the focus of considerable recrimination, primarily from angler and charter fishing groups in the U.S. which have had a historical antipathy to commercial fishing interests. This conflict is complex, dating from the 1960s and earlier, with the result in the United States that, in 2011, commercial fishing was mostly eliminated from Great Lakes states. One report suggests that battling between diverse fishing interests began around Lake Michigan and evolved to cover the entire Great Lakes region.[108] The analysis suggests that in the Lake Erie context, the competition between sport and commercial fishing involves universals and that these conflicts are cultural, not scientific, and therefore not resolvable by reference to ecological data.[109]
Sport fishing
The lake also supports a strong sport fishery. While commercial fishing declined, sport fishing has remained. The deep cool waters that spawn the best fishing is in the Canadian side of the lake.[110] As a result, a fishing boat that crosses the international border triggers the security concerns of border crossings and fishermen are advised to have their passport.[110] If their boat crosses the invisible border line in the lake, upon returning to the American shore, passengers will have to "drive to a local government reporting station and pose for pictures" to Customs officers by videophone.[110] There are cumbersome rules for fishing boat operators as well, who will have to fax passenger personal information to a government agency an hour before leaving; officers will be watching and doing spot checks from patrol boats and government aircraft".[110] Authorities in 2008 from the Pennsylvania Fish and Boat Commission have tried stocking the lake with brown trout in an effort to build what's called a put-grow-and-take fishery.[111] There was a report that charter boat fishing increased substantially on the American side, from 46 to 638 charter boats in operation in Ohio alone, during a period from 1975 to 1985 as pollution levels declined, and after populations of walleye increased substantially in the lake.[100] In 1984, Ohio sold 27,000 nonresident fishing permits, and sport fishing was described as big business.[100] In 1992, there were accounts of fishermen catching 8, 10, and 12 pound walleyes, and that the "runt of a five-man daily limit of 25 walleye might be a nuisance of 5 pounds."[112] It is possible to fish off piers in winter for a fish called the burbot, also known by pseudonyms such as eelpout, mudblow, lawyer fish, cusk, or freshwater cod which looks "ugly" but tastes great; the burbot make a midwinter spawning run and is reportedly one of "Erie's glacial relics."[99]

Ice fishing
In winter when the lake freezes, many fishermen go out on the ice, cut holes, and fish. It is even possible to build bonfires on the ice.[64] But venturing on Lake Erie ice can be dangerous. In a freak incident in 2009, warming temperatures and winds of 35 miles per hour and currents pushing eastward dislodged a miles-wide ice floe which broke away from the shore, trapping more than 130 fishermen offshore; one man died while the rest were rescued by helicopters or boats.[113]
The day began with fishermen setting down wooden pallets to create a bridge over a crack in the ice so they could roam farther out on the lake. But the planks fell into the water when the ice shifted, stranding the fishermen about 1,000 yards offshore ... When fishermen realized late Saturday morning that the ice had broken away, they began to debate the best way off. Some chose to sit and wait for authorities, while others headed east in search of an ice bridge ... Others managed to get to land on their own by riding their all-terrain vehicles about five miles east to where ice hadn't broken away. ... When the rescued fishermen made it to shore, authorities had them line up single-file to take down their names.—John Seewer, February 2009[113]

Agriculture

The lake's formerly more extensive lakebed creates a favorable environment for agriculture in the bordering areas of Ontario, Ohio, Michigan, Pennsylvania, and New York. The Lake Erie sections of western New York State have a suitable climate for growing grapes, and in Chautauqua County there have been many vineyards and wineries in the area as well as in Erie County in northwestern Pennsylvania.[114] Much grape juice is produced in this region.[114] The Canadian region of Lake Erie's north shore is becoming a more prominent wine region as well; it has been dubbed the Lake Erie North Shore, or LENS region, and includes Pelee Island,[115] and since it is farther north than comparable wine-growing areas in the world, the season is longer in terms of light.[116] A longer growing season due to the lake-moderated temperatures make the risk of early frosts less likely.[116]
The drainage basin has led to well fertilized soil. The north coast of Ohio is widely referred to as its nursery capital.[117]
Tourism
Diving for shipwrecks
Lake Erie is a favorite for divers since there are many shipwrecks, perhaps 1,400 to 8,000 according to one estimate,[39] of which about 270 are "confirmed shipwreck locations."[39] Most wrecks are undiscovered but believed to be well preserved and in good condition and at most only 200 feet (61m) below the water surface.[118] One report suggests there are more "wrecks per square mile" than any other freshwater location, including wrecks from Native American watercraft. There are efforts to identify shipwreck sites and survey the lake floor to map the location of underwater sites, possibly for further study or exploration.[119] While the lake is relatively warmer than the other Great Lakes, there is a thermocline, meaning that as a diver descends, the water temperature drops about 30 degrees Fahrenheit change (17°C), requiring a wetsuit.[118] One estimate is that Lake Erie has a quarter of all 8,000 estimated shipwrecks in the Great Lakes.[118] They are preserved because the water is cold and salt-free creating "intact time capsules down there".[118] Divers have a policy of not removing or touching anything at the wreck else the "next person won't be able to see it"; when artifacts were removed on occasion, it was met by "outrage" by the diving community.[118] The cold conditions make diving difficult and "strenuous" requiring divers with skill and experience.[118] One charter firm from western New York State takes about 1,500 divers to Lake Erie shipwrecks in a typical season from April through October.[118]
Among the diving community, they are considered world class, offering opportunities to visit an underwater museum that most people will never see.—reporter Shannon M. Nass of the Pittsburgh Post-Gazette, 2010[118]

In 1991, the 19th-century sidewheeler Atlantic was discovered.[120] It had sunk in a collision with the Ogdensburg, a steamship sometimes referred to as a "propeller" according to 19th-century parlance, in 1852, six miles (9.7km) west of Long Point, Ontario and survivors from the Atlantic were saved by the Ogdensburg.[120][121] One account suggests 130 people drowned[120] while another suggests about 20 drowned.[121] The aftermath of the disaster led to calls for authorities to seize captains of both ships so "that the cause of the collision may be correctly ascertained" as well as calls for more lifeboats and improved life preservers since the earlier ones proved to be "totally useless."[121] There was speculation that the sunken vessel had been a gambling ship, and therefore there might have been money aboard, but most historians were skeptical.[120] In 1998, the shipwreck of the vessel Adventure was the first shipwreck registered with the state of Ohio as an "underwater archaeological site"; when it was discovered that the Adventure's propeller had been removed and given to a junkyard, the propeller was rescued days before being converted to scrap metal and brought back to the dive site and back to its underwater home.[39] In 2003, divers discovered the steamer Canobie near Presque Isle, which sunk in 1921.[119] Other wrecks include the fish tub Neal H. Dow (1910), the Elderado "steamer-cum-barge" (1880),[119] the W. R. Hanna,[39] the Dundee which sank north of Cleveland in 1900,[39] the F. H. Prince,[39] and The Craftsman.[39] In 2007, the wreck of the steamship named after Mad Anthony Wayne was found near Vermilion, Ohio in 50 feet (15m) of water; the vessel sank in 1850 after its boilers exploded, and 38 people died.[122] The wreck belongs to the state of Ohio and "salvaging it is illegal" but divers can visit it after it is surveyed.[122] In addition, there are wrecks of smaller vessels, with occasional drownings of fishermen.[123]
The finding of the well-preserved wreck of the Canadian-built British troop transport warship Caledonia, sunk during the War of 1812, has led to accusations about plundering of the site and legal wrangling about whether the vessel should be resurfaced in time for the 2013 war's bicentennial.[124]
Research into shipwrecks has been organized by the Peachman Lake Erie Shipwreck Research Center, or PLESRC, located on the grounds of the Great Lakes Historical Society.[39] In 2008, the Great Lakes Historical Society announced plans to survey the underwater battle site of the Battle of Lake Erie in preparation for the bicentennial celebration of the battle in 2013.[39]
Public parks

There are numerous public parks around the lake. In western Pennsylvania, a wildlife reserve was established in 1991 in Springfield Township for hiking, fishing, cross-country skiing and walking along the beach.[125] In Ontario, Long Point is a peninsula on the northwest shore near Port Rowan that extends 20 miles (32km) into Lake Erie which is a stopover for birds migrating as well as turtles; one reporter found a "turtle-crossing" sign along the road; Long Point Provincial Park is located there and has been designated as a UNESCO Biosphere reserve.[22] In Ontario's Sand Hill Park, east of Port Burwell, there is a 450-foot (140m) high dune which is so steep it requires people to "crawl like crabs to the summit", although there are lake views from the top.[73]
Crystal Beach, in the village of Crystal Beach, Ontario, at the eastern end of the lake, is one of several South-facing beaches on the Canadian side. It is therefore well situated for sun-bathers, facing the sun from sunrise to sunset. The beach is gently sloping with no sharp drop-offs or rip currents, and is usually cooled by southwest breezes, even on the hottest days.
In southern Michigan, Sterling State Park has campgrounds, 1,300 acres (530ha) for hiking, biking, fishing, boating, with a sand beach for sunbathing, swimming, and picnicking.[126]
Biking
The New York Times reporter Donna Marchetti took a bike tour around the Lake Erie perimeter in 1997, traveling 40 miles (64km) per day and staying at bed and breakfasts.[22] They went through the cities of Cleveland, Erie, Windsor, Detroit and Toledo as well as resort towns, vineyards, and cornfields.[22] The trip highlights were the "small port towns and rural farmlands of southern Ontario".[22] There are few bike repair shops in Ontario on the route.[22]
Islands

Lake Erie islands tend to be in the westernmost part of the lake and have different characters. Some of them include:
Kelleys Island has activities such as beach lounging, hiking, biking, and viewing the deep glacial grooves in the bedrock limestone.[21]
Pelee Island is reached by ferry from Leamington, Ontario or by plane or ferry in Sandusky, Ohio and is the largest of the Lake Erie islands.[22] The island has a unique ecosystem with plants rarely found in Canada such as wild hyacinth, yellow horse gentian, and prickly pear cactus.[22] There are two endangered snakes including the blue racer and the Lake Erie water snake. Songbirds migrate there in spring, and monarch butterflies stop over during the fall.[22]
South Bass Island has the island-village of Put-in-Bay, Ohio which attracts young crowds who sometimes are prone to general merriment.[21] It has been described as a party island with scenic rocky cliffs with a year-round population in the hundreds that grows during summer.[21]

Water sports
Kayaking has become more popular along the lake, particularly in places such as Put-in-Bay, Ohio.[17] There are extensive views with steep cliffs with exotic wildlife and "100 miles of paddle-friendly shoreline."[17] Long distance swimmers have swum across the lake to set records; for example, a 15-year-old amputee swam the 12-mile (19km) stretch across the lake in 2001.[127] In 2008, 14-year-old Jade Scognamillo swam from New York's Sturgeon Point to Ontario's Crystal Beach and completed the 11.9-mile (19.2-km) swim in five hours, 40 minutes and 35 seconds, and also became the youngest swimmer to make the crossing.[128] It is illegal for swimmers younger than 14 to attempt such a crossing.[128] In Port Dover, Ontario, brave swimmers do high-dives at the annual Polar Bear Swim on the beach; in 2011, the water was 32°F (0°C), although the air was warmer, which did not deter 14-year-old youth Austin Merrell.[129] Currents can pose a problem, and there have been occasional incidents of drownings.[130][131]
Lighthouses

The lake is dotted by distinct lighthouses. A lighthouse off the coast of Cleveland, beset with cold lake winter spray, has an unusual artistic icy shape, although sometimes ice prevents the light from being seen by maritime vessels.[132]
Towns along the lake
A New York Times reporter, biking through the region in 1997, found the Ontario town of Port Stanley to be the "prettiest of the port towns" with a lively "holiday air" but no "ticky-tacky commercialism".[22]
Vineyards
There are numerous vineyards around the lake, including ones on Pelee Island which makes wines including pinot noir, riesling and chardonnay.[22]
Summer rentals
People can rent summer houses and cabins near the lake to enjoy the beaches, swimming, as well as be close to activities such as wine tours and fishing and water parks.[133] Presque Isle is a peninsula jutting out into the lake in northwestern Pennsylvania which has nice beaches, although there were incidents in 2006 when beaches had to be closed because of unexplained unhealthy water conditions with E. Coli bacteria.[95]
It was described as a "spit of sand, trees and swamp that arcs off the shore" with seafood restaurants and beautiful sunsets.[23] Pelee Island, Canada's southernmost point and only three miles away from Ohio, is a place that "forces you to do nothing":
I spent the next couple of hours riding that guy's creaky, brown three-speed across the flat, open island in a flawless summer breeze. I saw kilometres of gentle, swaying soybean fields. Occasional dense stands of trees. A red-brick schoolhouse attended by 10 children. A dozen cars – most of the drivers offering a wave. And ... that's about it. No stoplights. Few businesses other than a bakery, a few B&Bs, a small grocery and a gift store. Certainly no chains or corporations. And that's the point ... excitement comes in the form of a pilgrimage to the old stone lighthouse.—Josh Noel of the Nanaimo Daily News in 2010[134]

Pleasure cruises
Pleasure boat operators offer dinner cruises in the Cleveland area on the Cuyahoga River as well as Lake Erie.[135]
Folklore
Lake Erie Monster. There have been reports of persons spotting a creature akin to the Loch Ness Monster, but there have been no confirmed reports.[104] There were reports in 1990 of people seeing a "large creature moving in the water about 1,000 feet (300m) from their boat" described as black in color, about 35 feet (11m) long, with a "snakelike head", and moved as fast as a boat.[104] Five other people reported seeing something similar on three separate occasions but there is no scientific evidence of such a creature.[104] There is a beer named after the Lake Erie Monster as well as a hockey team.[136] There were reports of people spotting a sea creature in the 19th century which was sometimes called "Bessie" or "South Bay Bessie".[136]

Lake Erie Mirage Effect. There have been sporadic reports of people in Cleveland being able to see the Canadian shoreline as if it were immediately offshore, even though Canada is 50 miles (80km) from Cleveland. It has been speculated that this is a weather-related phenomenon, working on similar principles as a mirage.[137]
Shipping traffic

The lake has been a "bustling thoroughfare" for maritime vessels for centuries.[118][119] Ships headed eastward can take the Welland Canal[138] and a series of eight locks descending 326 feet (99m) to Lake Ontario which takes about 12 hours, according to one source.[22] Thousands of ships make this journey each year.[22] During the 19th century, ships could enter the Buffalo River and travel the Erie Canal eastward to Albany then south to New York City along the Hudson River. Generally there is heavy traffic on the lake except during the winter months from January through March when ice prevents vessels from traveling safely.[138] In 2007, there was a protest against Ontario's energy policy which allows the shipping of coal in the lake; GreenPeace activists climbed a ladder on a freighter and "locked themselves to the conveyor belt device that helps to unload the ship's cargo"; three activists were arrested and the ship was delayed for more than four hours, and anti-coal messages were painted on the ship.[139]
The ship traffic in Lake Erie being the highest among the Great Lakes[140] and roughest of the lakes has led to it having the highest number of known shipwrecks in the Great Lakes. There have been other accidents as well; for example, in 2010 according to The Star, crewmen from the freighter Hermann Schoening were sickened by phosphine gas which had been used to fumigate or control pests; rescuers took them by tugboat to receive medical attention.[141]
Ports

The Port of Cleveland generated over $350 million and over 15 million tons of cargo in a recent year. The current port facility is unable to handle larger cargo ships, and the cranes needed to lift goods such as steel to truck trailers are insufficient to meet current shipping standards.
Ferryboats
Ferryboats operate in numerous places, such as the Jet Express Ferry from Sandusky and Port Clinton. However, plans to operate a ferryboat between the U.S. port of Erie and the Ontario port of Port Dover ran into a slew of political problems, including security restrictions on both sides as well as additional fees required to hire border inspectors.[23] In particular, Canada was described as having a "sticky set of laws"; the project was abandoned.[23]
The Great Lakes Circle Tour is a designated scenic road system connecting all of the Great Lakes and the St. Lawrence River.[142] One reporter thought the roads on the Canadian side were narrower, sometimes without shoulders, but were less trafficked except for the roads around the Ontario towns of Fort Erie and Port Colborne.[22] Drivers can cross from the United States to the Canadian town of Fort Erie by going over the Peace Bridge.[22]
Lake Erie airspace

In 2004, debris from a plane carrying 9 people was found off Lake Erie isle.[143]
Border crossings
Since the border between the two nations is largely unpatrolled, it is possible for people to cross undetected from one country to the other, in either direction, by boat. In 2010, Canadian police arrested persons crossing the border illegally from the United States to Canada, near the Ontario town of Amherstburg.[144]
See also

Bass Islands
Cedar Point
Lake Erie AVA
List of lakes by area
List of lakes in Ohio
Maumee Bay

Great Lakes in general

Great Lakes Areas of Concern
Great Lakes census statistical areas
Great Lakes Commission
Great Lakes Waterway
Great Recycling and Northern Development Canal
Great Storm of 1913
International Boundary Waters Treaty
List of cities along the Great Lakes
Sixty Years' War for control of the Great Lakes
Snowbelt
Third Coast

View

Further reading
Assel, R.A. (1983). Lake Erie regional ice cover analysis: preliminary results  [NOAA Technical Memorandum ERL GLERL 48]. Ann Arbor, MI: U.S. Department of Commerce, National Oceanic and Atmospheric Administration, Environmental Research Laboratories, Great Lakes Environmental Research Laboratory.
Saylor, J.H. and G.S. Miller. (1983). Investigation of the currents and density structure of Lake Erie [NOAA Technical Memorandum ERL GLERL 49]. Ann Arbor, MI: U.S. Department of Commerce, National Oceanic and Atmospheric Administration, Environmental Research Laboratories, Great Lakes Environmental Research Laboratory.

 Geographic data related to  at OpenStreetMap

 – National Geophysical Data Center
Slate Magazine

What is the most common fish found in the Great Lakes?


The Byzantine Empire (the Eastern Roman Empire  during the medieval period, after the fall of the Western Roman Empire) following the Sack of Constantinople (1204) slowly collapsed by Ottoman expansion. After crisis of the Gothic Wars it managed to re-establish itself in a golden age under the Justinian dynasty in the 6th century, and during the Early Middle Ages it continued to flourish even after the Muslim conquest of the Levant and the constant threat of Arab invasion.
But in the High Middle Ages, under pressure from the Seljuk Empire, it suffered serious setbacks and fell into decline. After the Battle of Manzikert (1071) it lost control of Anatolia, and while the Komnenos dynasty restored a degree of stability in the 12th century with help from the First Crusade, the empire was captured and partitioned by the Crusaders themselves in the Fourth Crusade in 1204.
Even after Byzantine rule was restored in 1261, the empire was now a shadow of its former self, and after the end of the Crusades, the empire had little to set against the rise of the Ottoman Empire during the late medieval period, and was eventually conquered with the Fall of Constantinople in 1453.
Timeframes

The process by which the empire waned, and from when its decline can be traced, is a matter of scholarly debate. In some cases, the entire history of the Byzantine Empire has been portrayed as a protracted period of decline of the Roman Empire. This holds especially for Enlightenment era writers such as Edward Gibbon, author of The History of the Decline and Fall of the Roman Empire, published in six volumes between 1776 and 1789, whose view was coloured by pro-western or anti-clerical biases, and tended to see the whole ten-century empire as merely a sad codicil to the Roman Empire of Antiquity.
Late-20th-century and early-21st-century historians have instead emphasized the empire's remarkable resiliency and adaptability to change.[1][2][3][4]
The Byzantine-Arab Wars and the Battle of Manzikert have traditionally been considered the most significant. However, recent books by Paul Magdalino and John Birkenmeier have re-evaluated the position of the empire in the 12th century, citing the collapse under the Angeloi (1185–1204) as the most decisive turning point in the empire's fortunes. Although this view is not universally held, historians generally agree that after the Fourth Crusade in 1204, the empire was only a shadow of its former self.
The death of Michael VIII in 1282 marks the last period of Byzantine success on anything more than a minor scale. From this date onwards, the empire entered its final decline.
The history of the empire includes a number of periods of crisis, interspersed with periods of at least partial recovery:
The crisis of Late Antiquity, which saw invasions by the Visigoths, Huns, Alans, and Vandals across both the Rhine and Danube frontiers, sweeping through most of Europe
602  - Start of the Byzantine–Sasanian War of 602–628, which exhausted the Empire's resources and contributed to major territorial losses during the Muslim conquests of the 7th century.
The crisis of the 7th century, which saw Muslim conquest of the Levant and the Arab-Byzantine Wars
634  – Start of the Byzantine-Arab Wars
636  - The Battle of Yarmouk
The crisis of the 11th century, which simultaneously saw the  Norman conquest of southern Italy, the Pechenegs (in the Crimea and the Balkans), and the Seljuk invasion of Asia Minor and the devaluation of the nomisma
1025 – Death of the soldier-emperor Basil II
1071 – The Battle of Manzikert[5]
1176 - The Battle of Myriokephalon
1180 – Death of Manuel I Komnenos
1185 – Demise of the Komnenos dynasty
1204 – The Sack of Constantinople by the Fourth Crusade[5]
The crises of the 13th century, which followed the Sack of Constantinople and partitioning of the empire by the Fourth Crusade
The final decline during the Byzantine–Ottoman Wars.
Historical events
Collapse of the Western Roman Empire
In the 5th – 7th century, the Eastern Roman or Byzantine Empire was a continuation of the Roman Empire. The loss of the Western territories in the 5th century led to the loss of some important cities such as Rome. The creation of the Germanic states of the Franks, Visigoths, Ostrogoths and later of the Lombards out of the rubble of the Western Roman Empire meant that in time they would seek to challenge the authority of the Eastern Roman Empire. General Flavius Belisarius under Justinian I in the early 6th century made a serious attempt to recover the western half; however his gains were short-lived and poorly planned out – resources and troops that could have been used to defeat the Persians were diverted forcing the Byzantines into tribute and diplomacy to deal with this Eastern threat. The loss of the western territories led to the Patriarch of Rome achieving greater independence from Byzantium, which no longer provided adequate protection to the Pope. Consequently, the Holy See and Byzantium would have disagreements, culminating in the schism of 1054 and the disaster of the Fourth Crusade in the 13th century.
Rise of Islam
In the 7th – 9th century, Islam gave the Arabs a newfound zeal and desire to conquer. They expanded to the territories in the Levant and Egypt.
The Arab invasions led to the loss of Egypt, Syria, Palestine and for a short period of time, Crete, Sicily, Cyprus and Asia Minor. Though Asia Minor was recaptured and substantial parts of Syria and Mesopotamia either taken back or subjugated, Egypt remained firmly in Arab hands as did the rest of Palestine. The loss of Egypt was a major blow to the Byzantines since the province of Aegyptus had provided much of the Empire's manufactured goods and natural resources, especially grain, ever since the times of Roman Antiquity. Conversely the Arab acquisition of Egypt gave the Ummayad and later Abbasid Caliphates huge resources, meaning that the Byzantines had to direct large amounts of resources to stave off constant Arab incursions into Asia Minor and Syria. When the Fatimid Caliphate broke away from the Abbasids the Byzantines were able to launch successful offensives into Syria and Palestine, due to this division amongst their enemies.
Increasing Reliance on Foreign Military Intervention in Domestic Politics
As far back as the invasion of Africa by Belisarius, foreign soldiers were used in war.[6] While foreign military invention was not an all together new occurrence,[7] the reliance on it, and its ability to damage political, social, and economic institutions were dramatically increased in the 11th, 13th, 14th, and 15th centuries. The 11th century saw increasing tensions between Courtly, and Military factions.[8][9] Until the mid 11th century the empire had long been under the control of the Military Factions with leaders such as Basil II, and John I Tzimiskes,[10] however the crisis of Basil II's succession led to increasing uncertainty in the future of politics.[8] The army demanded Basil's daughters remain in power, leading to a number of marriages, and increasing power for the Courtly faction.[8] This culminated after the failed Battle of Manzikert. As civil wars broke out, and tensions between courtly, and military factions reached a zenith, an increasing demand for soldiers led to the hiring of Turkish Mercenaries to fight internal civil war.[11] These mercenaries aided in the Byzantine loss of Anatolia by drawing more Turkish soldiers in to the interior of the empire, and by giving the Turks an increasing presence in Byzantine politics. These interventions also led to further destabilization of the political system.[11][12]
Reliance on foreign military intervention, and sponsorship for political motives, continued even during the Komnenoi Restoration, Alexius I utilized Turkish mercenaries in the civil wars he participated in with Nikephoros III Botaneiates.[12] In 1204, Alexios IV Angelos relied on Latin soldiers to claim the throne of Byzantium, leading to the sack of Byzantium, and the creation of the successor states.[11] After the resurgence of the Byzantine Empire with the ascension of Michael VIII Palaiologos reliance on foreign sponsorship increased still more. At this time it was common for emperors to seek sponsorship from Venice, Genoa, and the Turks. This led to a series of disastrous trade deals with the Italian states; drying up one of the empire's final sources of revenue.[13] This further led to competition between Venice, and Genoa to get emperors on the throne who supported their respective trade agenda to the detriment of the other, adding another level of instability to the Byzantine political process.[13]
Seljuk conquest of Anatolia

In spite of its grievous losses of territory in Egypt and the Levant, the Byzantine empire successfully re-established itself against the threat of Islam  under the Macedonian dynasty in the 9th and 10th century.
But in the 11th century, a new threat arose as a consequence of the Turkic expansion out of Central Asia.
The Seljuks, a division of the Kankalis branch of Oghuz Turks, profiting from both the breakup of the Abbasid Caliphate and the absorption of the Byzantines with internal crisis and the loss of Italy to the Normans, managed to establish themselves in Asia Minor.
Following the Battle of Manzikert, the Byzantine Empire lost most of its territory in Asia Minor, and was in immediate danger of complete annihilation.
It recovered following the Komnenian restoration, as Alexios I Komnenos restored relations with the Papacy, and
requested aid against the Turks from  Pope Urban II at the Council of Piacenza in 1095. Later that same year, the pope preached the First Crusade at the Council of Clermont.
In the wake of the success of the First Crusade, the three competent Komnenian emperors, especially Manuel I Komnenos (r. 1143–1180), may have had the power to expel the outnumbered Seljuks, several factors combined to ensure that they never did so. Alexios was unable to derive much of the expected benefit from the  Crusade, though it did at least help him to recover Nicaea and western Asia Minor.
No emperor after the Komnenian period was in a position to expel the Turks from Asia Minor, while the preoccupation of the Nicaean emperors with the attempt to recover Constantinople meant that resources were diverted away from Asia Minor and towards the west.
The result was a weakening of the Byzantine defenses in the region, which, when combined with insufficient resources and incompetent leadership, led to the complete loss of all the empire's Asian territory to the Turks by 1338.

Though the Crusades assisted Byzantium in driving back some of the Turks, they went far beyond the military assistance envisaged by  Alexios I.
Instead of following the strategic necessities of the war against the Turks, the Crusaders were focussed on the quest of re-conquering Jerusalem,
and instead of returning territory to Byzantium, the Crusaders established their own principalities, becoming a territorial rival to Byzantine interests in their own right.
This was true already during  the Third Crusade, which induced emperor Isaac II Angelos to make a secret alliance with Saladin to impede the progress of Frederick Barbarossa, but open conflict between Crusaders and Byzantium erupted in the Fourth Crusade, resulting in the Sack of Constantinople in 1204. Constantinople was now itself a Crusader state, known as the Latin Empire in historiography, but from the Greek perspective as Frankokratia or "rule of the Franks". Vestiges of imperial power were preserved in minor principalities,   the Nicaean Empire, Trebizond and Epirus. Much of the Nicaean Emperors' efforts now went into combating the Latins, and even after Constantinople was returned to Greek rule  under the Palaiologoi in 1261, the Empire exerted much of its efforts into defeating its Latin neighbours, contributing to the eventual failure of the Crusades by 1291.
Final decline in the late medieval period
Throughout the 14th and 15th centuries the Empire suffered from many natural disasters, invasions and several coups.
Civil Wars
A series of societal infighting also weakened the Byzantine Empire's military power. There were two major civil wars during the late Byzantine Empire, one in 1321 another in 1341. These civil wars also severely diminished the Byzantines' military capabilities.
The civil war of 1321–1328 was led by a grandson of the Byzantine emperor Andronikos II who was supported by Byzantine Magnates who often clashed with the centralized authority of Byzantium. The Byzantine civil war of 1321–1328 was inconclusive and ended with Andronikos III being made co-emperor with his grandfather. This civil war allowed the Turks to make notable gains in Anatolia and set up their capital in Bursa 100 kilometers from Constantinople the Byzantine's capital. After the initial conflict Andronikos III dethroned his grandfather and became emperor.[14]
Following the death of Andronikos III in 1341, another civil war broke out which was to continue until 1347. When Andronikos III died he left his six-year-old son under the regency of Anne of Savoy. The de facto leader of the empire, John Cantacuzenus, who was not only a close associate of the deceased emperor but an extremely wealthy landowner, wanted to become regent.[15] However, things did not go his way and he was declared emperor in Thrace.[16] This conflict had elements of class warfare, in that the rich supported Cantacuzenus while the poorer folk supported the empress regent. The civil war of 1341–1347 saw exploitation of the Byzantine Empire by the Serbs, whose ruler took advantage of the chaos to proclaim himself emperor of the Serbs and Greeks. The Serbian king Stefan Uroš IV Dušan made significant territorial gains in Byzantine Macedonia in 1345 and conquered large swathes of Thessaly and Epirus in 1348.[17] Although Dusan would die along with his dream of a Serbian Greek empire in 1355,[18] Byzantium would still face a powerful Turkish state across the Sea of Marmara. Luckily for Cantacuzenus, he conquered Constantinople in 1347 and ended the civil war afterwards.[19] In order to secure his authority during the civil war, Cantacuzenus hired Turkish mercenaries. Although these mercenaries were of some use, in 1352 they seized Gallipoli from the Byzantines.[18] Although in 1354 the rogue mercenaries were defeated by western crusaders,[20] Turkish armies would eventually control many of the Byzantine Empire's once-held territories. These two monumental civil wars severely diminished the Byzantine Empire's military strength and allowed its opportunistic enemies to make substantial gains into Byzantine territory.
Rise of the Ottomans
The disintegration of the Seljuk Turks led to the rise of the Ottoman Turks. Their first important leader was Osman I Bey, who attracted Ghazi warriors and carved out a domain in north-western Asia Minor.[21] Attempts by the Byzantine Emperors to drive back the Ottomans were unsuccessful, and ceased in 1329 with the Battle of Pelekanon. Following a number of civil disputes in the Byzantine Empire, the Ottomans subjugated the Byzantines as vassals in the late 14th century and attempts to relieve this vassal status culminated in the Fall of Constantinople in 1453.
Structure of Byzantium
The Byzantine Empire's survival depended upon its administration and the logistics that enabled it to run the Empire. Though considered complex, its system was one more advanced than those practised by the Frankish Kingdoms in the West and one modelled by the Islamic Powers of the East. As the Empire evolved into an increasingly smaller and defensive state, the governing of the state changed as well. However, by the 14th century the burdens of running an Empire surrounded by many enemies became too much of a strain on Byzantium's increasingly smaller resources. By c. 1350's, the Byzantines lost Thrace to the Ottomans; thereafter Constantinople became the government's primary administrative region.
Politics of Byzantium
The Byzantine Empire experienced numerous civil wars. The defeats in the 7th and 12th centuries to the Arabs and Turks respectively speaking were in no small part assisted by numerous internal conflicts. The situation became worse later in the 14th and 15th centuries where Byzantine Emperors were forced to fight their own grandchildren/children, as in the cases of Andronikus II and Andronikus III.
Society of Byzantium
The Military of the Byzantine Empire was often smaller than that of its opponents and thus relied more upon strategy rather than brute strength to achieve success.[22][23] This was in part achieved by the logistics of the Byzantine administration which allowed it to utilize their troops as efficiently as possible. Taxes on the peasantry were collected at times of need so as to raise the supplies needed at the time.[24] However, this bureaucratic system was exploited by the social elite [24] whose increasing power challenged that of the Emperor. Whilst the Theme system worked well to provide efficient military service, it led to the decentralization of power leading to disastrous civil conflicts in the 11th century.
Furthermore, as the taxation system became ever more of a burden on the peasantry, the lower classes of the Empire began to resent the state. This contributed to the loss of Asia Minor in the 11th and 14th centuries owing to the arrival of the Turks.
The structure of the military

Another major factor in the decline of the Byzantine empire may have been the disintegration of its traditional military system, the 'theme' system. Under this arrangement, the empire was divided into several regions which contributed locally raised troops to the imperial armies. The system provided an effective means of cheaply mobilizing large numbers of men, and the result was a comparatively large and powerful force – the army of the theme of Thrakesion alone had provided about 9,600 men in the period 902–936, for example. However, the demise of the system made the organization of the Byzantine armies less self-sufficient.
The Byzantine military did not immediately collapse following the disappearance of the theme system. In the 12th century, the Komnenian dynasty re-established an effective military force. Manuel I Komnenos, for example, was able to muster an army of over 40,000 men. This was sufficient to ensure the empire's continued status as a great power for the duration of the Komnenian period. However, the Komnenoi never provided for a future that saw their decisive leadership replaced by incompetence. After the deposition of Andronikos I Komnenos in 1185, the dynasty of the Angeloi oversaw a period of military decline. From 1185 onwards, Byzantine emperors found it increasingly difficult to muster and pay for sufficient military forces, while the failure of their efforts to sustain their empire exposed the limitations of the entire Byzantine military system, dependent as it was on competent personal direction from the emperor. The culmination of the empire's military disintegration under the Angeloi was reached on 13 April 1204, when the armies of the Fourth Crusade sacked Constantinople and dismantled the Byzantine Empire.
Despite the restoration under the Palaiologoi, Byzantium was never again a great power on the scale of the past. By the 13th century, the imperial army numbered a mere 6,000 men, while the empire's territories had been reduced to little more than the lands immediately surrounding the Aegean sea.
Thus, it is possible to argue that the demise of the theme system was one of the most significant factors in the decline of the Byzantine empire. As one of the main institutional strengths of the Byzantine state, the theme system was never replaced by a viable long-term alternative. This left the empire lacking in underlying structural strengths. The result was an empire that depended more than ever before on the strengths of each individual emperor or dynasty. The collapse of imperial power and authority after 1185 revealed the inadequacy of this approach.
See also

Byzantine-Lombard Wars
Byzantine–Seljuq wars
Byzantine Empire under the Doukas dynasty
Byzantine Empire under the Angelos dynasty
Byzantine Empire under the Palaiologos dynasty
Notes

Bibliography

Alan Harvey, "Economic expansion in the Byzantine empire, 900–1200"
John Haldon, "The Byzantine Wars"
J.W. Birkenmeier, The Development of the Komnenian Army 1081–1180
Magdalino, Paul, The empire of Manuel I Komnenos 1143–1180

Runciman, Steven. The Fall of Constantinople 1453. Cambridge: Cambridge University Press, 1965.
Vryonis, Speros. The Decline of Medieval Hellenism in Asia Minor and the Process of Islamization from the Eleventh through the Fifteenth Century. Berkeley: University of California Press, 1971.