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City of Snohomish - NewsFlash

Posted on: September 5, 2019

Blackmans Lake Toxic Algae CAUTION Continues – 9/4/2019


Blackmans Lake is experiencing intermittent blue-green algae blooms along the shoreline. The algae may appear blue, green or white on the surface of the water, and is particularly concentrated near the shorelines.

Samples were collected on Wednesday, September 4th at the public boat launch by Snohomish County Surface Water Staff. The results indicate that the liver toxin, microcystin, was not present. This is below the WA State Department of Health's recreational guideline of 6 parts per billion (ppb). The CAUTION signs will remain posted at the at the public boat launch and Hill Park as long as algae scums are present.

The CAUTION signs advise lake users of the potential for exposure to toxic algae. It is especially important to avoid areas of algae scum because this is where the toxin levels are the highest. Also be aware that lake conditions and locations of scum can change from day to day.

CAUTION signs advise the following:

  • Do not swim in areas of scum
  • Do not drink lake water
  • Keep pets away from the lake
  • Clean fish well and discard guts
  • Avoid areas of scum when boating

Toxic algae can cause serious illness in humans who drink or play in affected waters. Pets that drink the water are at particular risk. If you or your pet are exposed to a blue-green algae bloom and have unexplained sickness or signs of poisoning, call your health care provider or veterinarian.

Please visit to see up-to-date testing information, sign up for alerts, and answers to commonly asked questions (choose the “Toxic Algae” link from the main page)..

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