Blue-Green Algae Bloom at Prior Lake

May 26, 2022 (updated Jun 27, 2022, 2:34pm)

As of June 27, this advisory for Prior Lake remains in effect. CRD staff continue to monitor water quality in the lake.

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

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.

Park 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 this 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.

To learn more about blue-green algae, please visit:

For more information on Prior Lake (located within Thetis Lake Regional Park), please visit: