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The original item was published from 9/21/2023 11:48:00 AM to 10/19/2023 5:05:02 PM.

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Park News

Posted on: September 21, 2023

[ARCHIVED] Gissberg Twin Lake North Toxic Algae WARNING 9/21/23

Gissberg North is experiencing a toxic algae bloom. The bloom looks like blue-green clumps on the lake bottom near the shoreline (see pictures below). There are also some large blue or black clumps floating in the lake.  

A sample was collected on Monday, September 18th, and screened for toxins. Sample results show that the liver toxin, microcystin, is present at levels that exceed the WA State Department of Health recreational guideline of 8 parts per billion for this toxin.

WARNING signs were posted at the lake which provide guidance for lake recreation (see adjacent sign). It is especially important to avoid areas of algae scum when recreating and prevent pets from drinking water with algae scum.  

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.

The pictures below show the dark green-blue or even black clumps found on the lake bottom at the Gissberg North shoreline. Some clumps were also found floating throughout the lake.

Toxic algae bloom in Gissberg North 9/21/23

Toxic algae bloom in Gissberg North 9/21/23



Please visit https://snohomishcountywa.gov/1959/Algae-Toxic-Algae 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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