Three dogs have died after ingesting the water at Quamichan Lake over the last couple of weeks.
The Municipality of North Cowichan is advising the public about a blue-green algae bloom at the Lake near Art Mann Park and signs have been posted.
Lake visitors are being advised to steer clear of the areas that have a visible blue-green sheen, which appears as a surface scum of the lake.
The Municipality is advising pet owners to keep their dog on a leash and prevent them from drinking or swimming in the water.
The Quamichan Watershed Stewardship Society and the Municipality will be meeting in the next couple of weeks to talk about the deteriorating quality of water in the lake.
Algae blooms have occurred in Quamichan Lake a number of times over the past few years, likely as a result of the build up of nutrients in the water.