Green Lake has joined 14 other lakes in the state with elevated levels of toxic algae, according to the state Department of Ecology.

The Seattle Parks and Recreation is urging people and pets to not swim in the lake and avoid any other contact with lake water.

Green Lake will be resampled in the coming week.

For people, toxic algae that produces nerve toxins and liver toxins  can mean skin rash, hives and itchy eyes and throat, according to the state Department of Health.

For pets, it can mean vomiting, seizures and convulsions that develop within 15 to 20 minutes. Although not common, over the years there have been reports of dogs dying after exposure to the toxic algae.

A Sept. 27, 1997, Seattle Times story told of a woman and her golden retriever wading into Lake Sammamish (currently not listed among the lakes with elevated levels of toxic algae). Within hours, the dog began heaving and coughing, and then died.

The woman said that over the years, the green slick at the lake had been a common sight during the balmy days of summer and early fall. She said, “‘Had I known that I was swimming in toxic algae, if that was the case, I wouldn’t have been in there.’”


There have been no recent news or state Department of Health reports of animal deaths as a result of toxic algae.

Other westside lakes with elevated levels of toxic algae are Lake Fenwick, Spanaway Lake, Silver Lake, Ohop Lake and Rapjohn Lake in Pierce County; Pass Lake in Skagit County and Lake Terrell in Whatcom County.

Toxic algae actually isn’t an algae but a bacteria that has blue-green blooms and so looks like algae. Its scientific term is cyanobacteria, with “cyan”derived from ancient Greek and meaning blue-green.

There are the thousands of cyanobacterial species, and roughly 200 are known to be toxic, according to an April 2018 paper published by the American Veterinary Medical Association.

Most cyanobacterial blooms occur during warm summer and early fall months but in Washington, toxic blooms also occur during colder winter months.

“It is possible that a bloom can be found somewhere in Washington nearly every month,” says the Department of Health.


If you think a lake near you might contain toxic algae, the state website tells how to collect and send a sample for free analysis at its laboratory. Because this is scientific analysis, “It is very important for you to carefully follow the directions,” says the website.

They’re quite astounding forms of life, the cyanobacteria.

They live in the water, and can manufacture their own food through photosynthesis.

“Cyanobacteria were ancient when our ancestors were taking their first tentative steps millions of years ago … [they] oxygenated the earth’s atmosphere, creating an environment that enabled the evolution of animal life,” says the American Veterinary Medical Association paper.

The paper says algae blooms occur in water containing high concentrations of nitrogen or phosphorus, of which the primary sources are human and animal waste, as well as fertilizers. It also cites climate change. The blooms have been found more and more in water supplies where blooms didn’t occur so much before, says the paper.

“You may think of cyanobacteria as primitive organisms, but I think of them as organisms that have had 3 billion years to figure out how to get it right. They’re very advanced,” the paper quotes Greg Boyer, director of the Great Lakes Research Consortium and a professor of biochemistry at State University of New York.