News Flash

City of Snohomish - NewsFlash

Posted on: December 9, 2020

Toxic Bloom of Blue-Green Algae

Blue-Green Algae

Blackmans Lake is still experiencing a blue-green algae bloom with scum accumulating along the shoreline. The algae scum looks like green paint floating on the surface of the water.

The State sampling program for toxins has closed for the winter so no samples will be taken.

Please assume that toxins are present where there is scum in the absence of testing.. 

WARNING signs were posted at the public access sites at the boat launch and Hill Park. The signs provide guidance for lake recreation (see sign below). It is especially important to avoid areas of algae scum because this is where the toxin levels are the highest.

The WARNING signs advise the following:

  • Do not swim in the lake
  • 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. Find out more about toxic algae by visiting

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