The Capital Regional District is advising Thetis Lake Regional Park visitors to avoid both the upper and lower sections and to keep animals on a leash to prevent them from drinking or swimming in the lake.
In a public service advisory released Tuesday, the CRD warned that samples taken from Thetis Lake have tested positive for blue-green algae and associated cyanotoxins.
Ingesting water containing blue-green algae may cause a range of symptoms, including headaches or abdominal pain in humans. It can also lead to lethal liver damage in dogs.
The algae usually produces a visible blue-green sheen, which can appear as surface scum. However, the CRD warns not all blooms are easy to see and toxins can still be present in the water even if you cannot see them.
Algal blooms can occur at any time, although blooms typically occur from November to March.