Big Lake Algae Bloom

A sign posted at the state Department of Fish & Wildlife boat ramp on Big Lake advises against swimming due to an algae bloom in the lake.

BIG LAKE — A potentially toxic algae that thrives during extended warm weather is being seen in Big Lake, prompting Skagit County Public Health to caution against contact with the water and to use extra care when preparing fish caught from the lake.

While the toxin levels in water samples taken Aug. 15 and Aug. 20 were not yet concerning to human and animal health, the local health department said in a statement Friday that conditions can change rapidly.

When toxins produced by the algae reach certain levels, exposure to the water or contaminated fish can cause nerve or liver poisoning, resulting in illness for humans and potentially death for animals, according to the state Department of Health.

Nerve poisoning symptoms including numbness, tingling and dizziness can occur within 20 minutes. Liver poisoning symptoms of abdominal pain, vomiting and diarrhea can occur hours or days later.

Although dangerous levels of the toxins haven’t been detected in Big Lake, the county is urging the community to take precautions as if they have been: avoid contact with the water, keep pets away from the water, and gut and wash fish well before consuming.

The algae bloom was discovered in mid-August by state Department of Ecology staff visiting the lake for an invasive plant survey.

“It was quite obvious,” Ecology blue-green algae expert Lizbeth Seebacher said of seeing discoloration on the water. “At the boat launch I could see something starting ... but when we got out on it in the south end of the lake it was pretty extensive.”

Blue-green algae blooms have been seen in Big Lake before, at least several times between 2013 and 2016, according to state Department of Ecology data.

“(In Skagit County) Big Lake is the big one — excuse the pun,” Seebacher said.

As Ecology’s project manager for disseminating funding to address blue-green algae (also called cyanobacteria), she’s seen blooms occur in various parts of the state — and noted that they are on the rise due to climate change and increasing development that brings septic systems, fertilizers, animals and other nutrient-bearing materials to areas near lakes.

“It’s definitely increasing ... throughout the country, not just in Washington state,” Seebacher said. “Here we are having warmer and drier springs, so that is causing the season to start earlier and persist well into the fall.”

When blooms occur — typically after extended periods of warm, sunny weather as well as when excess nutrients build up in the water — the algae can be visible as a patchy film, oily sheen or even paint spill-like layer on the water’s surface, according to Washington State Toxic Algae, a web page where various agencies compile data on freshwater algae blooms.

That web page includes data for Big Lake, as well as 10 other Skagit County lakes and a pond where blooms have been documented. Local lakes impacted by blue-green algae blooms in recent years include a cluster of six on Fidalgo Island as well as Big Lake, Clear Lake, Lake Cavanaugh, Lake McMurray and Lake Sixteen.

Seebacher said that data may not be complete, but she and Skagit County Environmental Health Program Manager Polly Dubbel agreed it is the best available.

The algae blooms documented in area lakes appear to occur sporadically, with some lakes seeing blooms several years in a row, some seeing only a single bloom years ago and some seeing blooms every few years.

In all, blooms have been recorded in Skagit County throughout much of the year, excluding March through May, according to the data.

Blooms in Big Lake tend to occur between July and October and have yet to reach dangerous levels of toxins.

Some samples taken from Fidalgo Island’s Heart Lake in 2012 and 2014 and Lake Erie in 2015 have reached potentially dangerous levels, according to the data.

Skagit County Public Health and Deception Pass State Park have issued various warnings and recreation closures over the years, including for Pass Lake in the state park.

Skagit County Public Health’s Dubbel said she is not aware of any other blooms in local lakes this summer.

— Reporter Kimberly Cauvel: 360-416-2199,, Twitter: @Kimberly_SVH,

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