The level of toxins in the algae at Green Lake has increased and has prompted parks and Public Health officials to close the lake to swimming and water contact for people and dogs.
People and pets should not swim, wade or play in the lake. Dog owners should be especially cautious not to allow animals to go in or drink from the lake. If there is water contact for a pet, it is important to rinse well to remove all algae.
Symptoms of illness from contacting the toxins in water are eye, nose, and mouth irritation and skin rash. If accidental contact occurs, use clean water to promptly rinse skin. Swallowing the toxins may cause abdominal pain, diarrhea vomiting and in severe cases liver damage. If symptoms occur after swallowing lake water, park users should consult a health care professional or veterinarian immediately. Pets are at highest risk.
Tests have revealed that high levels of toxins are currently found in the algae and are higher in areas where algae collect. King County Department of Natural Resources has been conducting weekly testing of water at various locations around Green Lake as well as scum samples submitted through the State Toxic Algae Program. After each test, the information is reviewed by Public Health – Seattle & King County.
The lake remains open to fishing (though fish should be thoroughly cleaned) and boating in stable boats. Avoid areas of scum when boating.
Seattle Parks and Recreation’s lifeguarded beaches closed for the season on Sept. 1.
A warm, dry summer has promoted the algae bloom, and continued warm weather continues to promote it. Blooms have been known to last into November in particularly warm autumns, and typically disappear as the weather gets colder.
Toxic algae blooms appeared at Green Lake in 1999, 2002, 2003, 2012 and in 2013, resulting in warnings to the public about exposure to the algae. Intense blooms of blue-green algae have occurred in Green Lake since 1916. Phosphorus released from the bottom sediments stimulates algae growth. 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 mostly good since 2004.
Green Lake is home to cyanobacteria, also known as 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.
For more information on cyanobacteria, please visit Washington Department of Health toxic algae website.
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