The rivers and streams that flow to Lake Superior through Pictured Rocks National Lakeshore have a relatively steep gradient and are rather short, because the water drainage divide in the area is much closer to Lake Superior than to Lake Michigan.
The steep gradient includes waterfalls, where the streams drop over erosion-resistant cliffs and escarpments. The more prominent waterfalls within the lakeshore are Munising, Miners, Mosquito, Bridalveil, Chapel, Spray, and Sable Falls. Especially noticeable at the waterfalls is the brown "tea" color of the water due to humic acids that originate from decaying vegetation in the headwaters.
The discharge (rate of flow) of the streams is highest in the late spring and early summer following snowmelt. In addition, these streams are very responsive to rainfall, and will rise immediately following a significant rain. Discharge can double for a day or so after a rainstorm.
Miners River is the longest and largest river in the lakeshore. Its discharge near the mouth averages 46 cubic feet per second during June and drops to an average of 21 cubic feet per second in late summer and fall. The Hurricane and Mosquito Rivers have similar discharges during spring and early summer (19 cubic feet per second), but that of the Mosquito River drops more significantly as the summer progresses.
Munising, Chapel, Spray, Sevenmile, Beaver, Rhody, Sullivan, and Sable Creeks are shorter and carry less water. Beaver Creek and Sable Creek flow from lakes and have more stable discharges, because the lakes buffer the effects of precipitation.
The substrates of the streams are variously composed of cobble/gravel, sand, and bedrock. The substrate in depositional areas along the banks and upstream from beaver dams is mud/silt. Most pools are formed by the force of water flowing over trees that have fallen into the streams.
The quality of the water of the inland lakes, rivers, and streams is directly related to the watersheds they drain. The majority of the shoreline zone's rivers and creeks have headwaters that occur in the Inland Buffer Zone and the surrounding region. In general, the current water quality of these headwaters is considered healthy; however since management of areas outside of park boundaries can affect the quality of the national lakeshore's water bodies, continued monitoring is necessary.
Within park boundaries, staff conduct water quality testing in various streams, survey aquatic wildlife populations, and monitor for invasive species.
More than 170 taxa of aquatic macroinvertebrates have been identified from the streams of Pictured Rocks. These include larval and/or adult water bugs, water beetles, caddisflies, stoneflies, dragonflies/damselflies, mayflies, fishflies/alderflies, true flies, riffle beetles, aquatic earthworms, scuds, leeches, snails and limpets, and crayfish. The presence of caddisfly, stonefly, and mayfly larvae indicate that streams here are of high quality and are in good ecological health.