Blue-Green Algae Bloom at Prior Lake

Aug 03, 2021 (updated Sep 28, 2021, 12:16pm)

As of Sept. 28, this advisory remains in effect. CRD staff will continue to monitor water quality in Prior Lake.

The Capital Regional District (CRD) advises, in consultation with Island Health, that there is a blue-green algae bloom at Prior Lake, located in Thetis Lake Regional Park.

Blue-green algae can produce cyanotoxins. Visitors are advised to avoid swimming at Prior Lake 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 that appears as surface scum. Not all blooms are easy to see and toxins can still be present in the water even if you cannot see the blooms. 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.

Please visit for updates on the status of this algae bloom. To learn more about blue-green algae visit our website

Thetis Lake Regional Park map (PDF)