TUALATIN -- A potentially toxic blue-green algae bloom, "thicker than clam chowder" in one spot, has laced an 11-mile stretch of the Tualatin River between Sherwood and Lake Oswego.
The U.S. Geological Survey in Portland is expected to receive test results today on whether the algae is toxic. Tests earlier this week indicated that the main type of algae present is one that can produce toxins.
Officials are asking the public to avoid contact with the Tualatin River water and to keep pets and children away. Residents should wash with soap if they do come into contact with it.
Eight or nine dogs in Oregon die annually from contact with water infected with blue-green algae, according to the USGS.
The clumpy algae was first spotted by Roy Rogers Road near Sherwood on Monday before traveling downstream as far as Stafford Road near Lake Oswego. It is most pronounced near Tigard and Tualatin and was akin to clam chowder Wednesday near Jurgens Park in Tualatin, said Brian Wegener, a watershed watch coordinator for Tualatin Riverkeepers.
Blue-green algae, despite its common name, is not algae, but a type of bacteria that turns sunlight into energy. A bloom occurs when algae multiply rapidly and, in this case, has turned stretches of the Tualatin into thick, fluorescent blue mats.
"It was pretty nasty," Wegener said. "It kind of looks like somebody dumped some aqua blue latex paint in the water."
Clean Water Services on Thursday more than tripled the amount of water it releases from Hagg Lake to 45 million gallons a day. Extra water will be released throughout the weekend, spokesman Mark Jockers said.
"What that water will do is cool the river off and slow the algae growth and, hopefully, push the algae out of the system," he said.
Experts suspect the bloom could be caused by a rise in the water temperature and the amount of organic material in the water.
Blue-green algae blooms have not been seen in decades, ever since nearby sewage treatment plants went online, two experts said.
It's unclear if the river would be closed in the event that the algae proves toxic.
Various forms of toxic blue-green algae, if swallowed, may cause diarrhea, nausea, fainting and paralysis. Skin contact can cause rashes or irritation.
In a separate case, city of Lake Oswego officials have asked residents to conserve water for about a week because nontoxic algae in the Clackamas River was clogging intake screens of the city's water treatment plant.
Three water treatment plants along the Clackamas River have found nontoxic green algae sticking to intake screens in the past two weeks.
--Yuxing Zheng; email@example.com