The North Bay Parry Sound District Health Unit is advising residents to be wary in the West Arm of Lake Nipissing.
Health officials say a bloom of blue-green algae was discovered in the West Nipissing region.
Owners of private water systems in that area should not use water from the lake for cooking, drinking or bathing.
Boiling water will not destroy the toxins.
You should avoid swiming in the water or letting pets or livestock drink from it either.
Health officials advise avoiding eating fish from that portion of the lake as well.