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Green Lake closed to swimming and sailboarding because of toxic algae bloom

A toxic algae bloom on Green Lake means no wading, swimming, sailboarding or allowing your pets to drink the water for the time being. Boating and fishing are still allowed.

The closure could take weeks or months, depending on how long it takes the algae to go away. The last time the lake was closed due to toxic algae blooms was 2003.

Warm, dry weather will promote the continuation of the bloom. Blooms have been known to last into November in particularly warm autumns, and typically disappear as the weather gets colder.

The toxin was found in an algae scum accumulation at a level of 34 micrograms per liter, well above the state recommended recreational guideline of 6 micrograms per liter. The initial test was performed by the King County Environmental Laboratory under the auspices of the Washington Department of Ecology’s algae program.

A King County scientist has taken further samples from several scums found around the lake, and submitted them under the same program for verification. Further monitoring will be conducted on the water at least once a week. Parks will reopen the lake when the evidence of toxin falls below the draft recreational guideline.

Treating the lake with alum inactivates the phosphorus that is released from the bottom sediments and prevents stimulation of the algae growth. Green Lake was successfully treated with alum in 1991 and 2004. The water quality improved for several years following treatment on both occasions, and has been very good since 2004.

Lake is home to photosynthetic cyanobacteria, or “blue-green algae” that are regularly present in small numbers. When nutrients are plentiful and the weather is warm, the conditions are right for an algae bloom to take place. Winds can concentrate the buoyant cyanobacteria into accumulations or scums along the shoreline, which may increase the amount of toxin that could be ingested by pets or people using the lake recreationally.

Symptoms of illness from liver toxin are flu-like and may include abdominal pain, diarrhea and vomiting. If symptoms occur after ingesting lake water, park users should consult a health care professional immediately.