Blue-Green Algae Bloom

Aug 15, 2023 (updated Sep 01, 2023, 11am)

The blue-green algae bloom at Prior Lake remains in effect. People and pets should continue to avoid swimming in the lake.

The Capital Regional District (CRD), in consultation with Island Health, advises that the blue-green algae bloom at Prior Lake, located at Thetis Lake Regional Park remains in effect. Blue-green algae can produce cyanotoxins. Visitors are advised to avoid swimming at these beaches 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.

Water sampling occurs twice in the first week after a bloom is no longer visible, and will continue until two consecutive water samples indicate levels below the threshold for blue-green algae producing toxins (<100,000 cells/mL). The CRD then consults with Island Health, and the advisory is lifted if Island Health confirms that the bloom is no longer a risk. The CRD will remove the temporary caution signs from around the lake, and will lift the advisory.

Please visit and Twitter @crd_bc for updates on the status of this algae bloom. To learn more about blue-green algae visit these sites: