Prior Lake at the north end of Thetis Lake Regional Park has tested positive for a type of blue-green algae that produces cyanotoxins.
As a result visitors are advised not to swim at Prior Lake, and to keep animals on a leash to keep them from drinking the water or swimming in the lake.
The algae usually produce a visible blue-green sheen, which appears as surface scum. Not all blooms are easy to see and toxins can still be present in the water even if you can't see the blooms -- which are unpredictable and may occur at any time.
The algae are known toxin producers and the compounds have been detected previously at Thetis Lake.
Ingesting water containing these cyanotoxins can cause a range of symptoms, including headaches and abdominal pain in humans, and can lead to lethal liver damage in dogs.
There are no signs of blue-green algae at Upper or Lower Thetis Lake.