As of October 9, 2026, the advisory for Thetis Lake has been lifted. The advisory remains in place for Prior Lake, Beaver Lake and Elk Lake.
The blue-green algae advisory is now lifted for the main beach at Lower Thetis Lake located in Thetis Lake Regional Park. Water samples collected indicated a “below detection limit” result for cyanotoxins. The extended absence of blue-green scum combined with test results are good indicators that the bloom is over.
However, please note that there is still an active advisory in effect for Prior Lake located in Thetis Lake Regional Park, for the Brookleigh Boat Launch at Elk Lake, and for Beaver Lake located in Elk/Beaver Lake Regional Park.
Blue-green algae can produce cyanotoxins. Visitors are advised to avoid contact with blue green algae and to keep animals on a leash to prevent them from drinking or swimming in the lake until the advisory has been lifted.
The algae usually produce a visible blue-green sheen, which appears as surface scum on the water. Not all blooms are easy to see, and toxins can still be present in the water even if you cannot see a bloom. Blooms are unpredictable and may occur at any time.
These algae are known toxin producers. Ingesting water containing these cyanotoxins may cause a range of symptoms, including headaches and abdominal pain in humans, and can lead to lethal liver damage in dogs.
To learn more about blue-green algae visit these sites:
