The CRD, in consultation with Island Health, advises that there is a blue-green algae bloom at Durrance Lake within Mount Work Regional Park.
The algae usually produces a visible blue-green sheen, which appears as surface scum on the water. But not all blooms are easy to see and toxins can still be present in the water.
CRD says visitors should avoid contact with the algae and to keep animals on a leash to prevent them from drinking or swimming in the lake until the advisory has been lifted.
Symptoms include headaches and abdominal pain in humans, and can lead to lethal liver damage in dogs.