Microcystins halt recreational activity in areas of Canyon Lake

Danger signs posted at Happy Camp warn people to say out of the water. Photo by Canyon Lake Insider.

Editor’s note: The POA received the latest results back and said, “Both areas have tested within a safe level to be reopened in time for the Memorial Day weekend.”

Water samples taken on May 8 from Happy Camp, Sierra Park, Sunset Beach, Indian Beach, and Holiday Harbor revealed elevated results for microcystins that were in the “danger” range on that date. As a result, recreational activity in the water at Sunset Beach and Happy Camp is prohibited. Holiday Harbor tested at the caution level. Warning signs are posted at these locations.

“Note that the current results are from May 8, 2023, and do not necessarily represent conditions anywhere else on the lake, or that the entire waterbody is affected,” the POA said in a news release.

The sample was done prior to last week’s alum treatment. New samples were taken and rushed to a lab in Sacramento for further testing. Those results are expected back on Friday, according to the Canyon Lake POA.

Microcystins are toxins produced by cyanobacteria. Cyanobacteria are known as blue-green algae and are ubiquitous in surface water when conditions are favorable for the growth and formation of algal blooms.

Harmful algae or cyanobacteria can look like foam, scum, paint, or mats on the surface of the water and can be different colors. These blooms can produce toxins that make people and animals sick. People who drink or swim in water that contain high concentrations of cyanobacteria or cyanobacterial toxins may experience gastroenteritis, skin irritation, and allergic responses.

For more information about harmful algal blooms, visit


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