Friends of Green Lake have blown the whistle on potentially toxic algae bloom in the lake, leading to a closure of the lake to some uses.

Gayle Garman, president of Friends of Green Lake notes that it was monitoring of the lake's water quality by the group that first alerted Seattle Parks and Recreation to the situation. The group demonstrated within 10 hours of the bloom's appearance that the algae toxin, microcystin A, was at greater than 3 parts per billion, leading the parks department to call for the partial closure.

Water quality monitoring by Friends of Green Lake lead to detection of toxic algae bloom at the lake, leading to a partial closure for some recreational uses.

Photo taken of the bloom by Gayle Garman on Oct. 1

The Seattle Parks and Recreation Department today announced a partial closure of the lake to wading, swimming and boating, and other activities in which people are likely to get wet, such as sailboarding. Dog owners also are cautioned against letting their dogs drink from Green Lake.

The lake remains open to fishing and other forms of boating.

The closure is in effect until the algae bloom completes its life cycle, which could take weeks, or months, if weather remains warm.

Warm, dry weather promotes the continuation of the bloom. The toxin was found in an algae scum accumulation above the state recommended recreational guideline. The lake has been closed in 1999, 2002 and 2003 for toxic algae blooms. Intense blooms in the lake have been recorded since at least 1916.

Treating the lake with alum helps suppress the bloom, which can cause flu-like symptoms, diarrhea and vomiting. Anyone with such symptoms after ingesting lake water should consult a doctor.

For more on alum treatments and toxic algae blooms and Green Lake see my stories in The Seattle Times.