Blue-green Algae Confirmed In Three Mile Lake And The Clark Falls Area Of Lake Rosseau


The Simcoe Muskoka District Health Unit (SMDHU) has been advised by the Ministry of Environment, Conservation and Parks (MECP) that laboratory tests have confirmed the presence of a blue-green algae bloom in Three Mile Lake and the Clark Falls area of Lake Rosseau.

Wind and water currents can change the location of algae blooms, which may make the water look bluish-green, or like green pea soup or turquoise paint, a caution is therefore being issued around both lakes. Swimming and other water sport activities should be avoided in areas where the blue-green algae bloom is visible.

The health unit warns residents around Three Mile Lake and the Clark Falls area of Lake Rosseau to avoid using the lake water for drinking or food preparation, including breastmilk substitute (infant formula).  Boiling the water will not destroy the toxins, and home treatment systems should not be relied on.

Exposure to blue-green algae, whether for drinking, swimming, cooking or through eating fish caught from the lakes, may result in illness. Adverse health effects are mainly caused by drinking water that is contaminated with blue-green algae toxins. Symptoms from consuming toxins can include headaches, fever, diarrhea, abdominal pain, nausea and vomiting, and can be more serious if water is swallowed in large quantities.

SMDHU and the MECP will continue to monitor both lakes and updates will be posted on the health unit’s website at

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