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Blackman Lake under toxic algae watch

SNOHOMISH — Toxic blue-green algae spotted on Blackman Lake Monday, July 25 prompted the city to put up warning signs against swimming in the water.
Another round of sample testing is scheduled for this week, city spokeswoman Shari Ireton said.
Until the lake is determined safe, the city asks that people take caution. Pets should stay out, too, and any fish caught to eat should be cleaned thoroughly.
Yellow warning signs that are about 12 inches by 18 inches, or about the size of the front page of a Tribune newspaper, are posted at Hill Park and Ferguson Park. At Hill Park, they’re posted at the entry to both fishing docks and on an information booth about the lake’s watershed.
Two sets of samples collected Sunday, July 24 for lab testing showed toxin levels within state recreation guidelines.
One sample registered anatoxins of 0.019 micrograms per liter. The state recreation guideline is no more than 1.000 micrograms per liter.
Blue-green toxic algae sometimes looks like a paint spill on the water. Non-toxic algae looks like a mat.
Anybody can report an algae bloom at
The lake is often treated to control algae blooms and invasive water lilies.
The lake last received an aquatic pesticide treatment June 29, a state Department of Ecology spokeswoman said. That was an application on 1.25 acres of the 61-acre lake which was “treated with 32 ounces of Imazapyr to control non-native lily pads,” a second Ecology spokesperson said.
Imazapyr is a nonselective herbicide; nonselective meaning it kills any plant it contacts.
Tight permit controls under Ecology regulate pesticide applications.
A future treatment should occur before Sept. 30, Ecology said.
In 2021, Blackman Lake received three such treatments.

In related news

The city is looking to hire a diver to manually pull invasive curly leaf pond weed in the lake this year. This weed first was spotted in the lake in 2021.

Michael Whitney photo
This is how the warning sign looks.

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