STANWOOD — Signs have been posted warning people not to swim or water ski at Lake Ketchum north of Stanwood after an outbreak of blue-green algae covered parts of the water with an unsightly scum.
The yellow-and-black signs warn people not to ingest the water, to keep pets away from the lake and avoid areas of scum on the lake while boating.
Blue-green algae is actually bacteria. Health officials say tests found levels of the toxin created by the bacteria were high enough to be considered a health risk.
The toxin created by the bacterium, called microcystin, can sicken people and animals if ingested at high enough levels.
It can cause allergic reactions, skin rashes, hives, itchy eyes and an itchy throat to people who swim in the water, said Joan Hardy a toxicologist for the state Department of Health.
Pets have died after drinking the unhealthy water at other lakes in Washington, she said.
The outbreaks can also kill fish.
Test results on water samples taken from Lake Ketchum results show microcystin concentrations of 416 parts per billion. That’s the highest reading that’s been recorded at that lake, Marisa Burghdoff, a water quality analyst for Snohomish County, said Friday.
Recommendations to avoid swimming, boating and other activities are posted on Washington lakes when microcystin levels reach at 6 parts per billion.
A volunteer who monitors the lake first notified Snohomish County last week about algae growing on the water, Burghdoff said.
Follow-up tests will be done weekly to monitor the lake’s condition, she said.
The lake is one of three in Snohomish County being tested each week for water quality, she said.
Algae blooms most often occur in the summer. They are caused by increased nutrients in the lake, warm temperatures, increased light and wind patterns. The outbreaks can last for several weeks.
Reporter Sharon Salyer: 425-339-3486 or salyer@heraldnet.com.
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