MUSKOKA — Waterfront residents in a couple of north and south Muskoka lakes are being warned about blue-green algae blooms this weekend.

So think twice about a quick dip before closing up the cottage.

The health unit said today that those in Gravenhurst on Kahshe Lake should take caution.

That word comes a day after those staying on Three Mile Lake in the Township of Muskoka Lakes received the same news yesterday.

The Simcoe Muskoka District Health Unit asks them to exercise caution where blue-green algae is visible and to take the following precautions:

  • Do not use the lake water for the preparation of infant formula
  • Do not allow pets or livestock to drink or swim in the water where an algae bloom is visible
  • Be cautious about eating fish caught in water where blue-green algae blooms occur
  • Do not use herbicides, copper sulphate or other algaecides that may break open algae cells and release toxins into the water
  • And avoid swimming and other water sport activities where an algae bloom is visible.

Blooms may make the water look bluish-green, or like green pea soup or turquoise paint.

Many species of blue-green algae (also called cyanobacteria) have the potential to produce toxins that are harmful to the health of humans and animals. The Ministry of Environment, Conservation and Parks will be further analyzing samples to determine the presence of any toxins.

Symptoms from consuming toxins from a blue-green algae bloom can include headaches, fever, diarrhea, abdominal pain, nausea and vomiting, and can be more serious if water is swallowed in large quantities.

The health unit and the Ministry of Environment, Conservation and Parks will continue to work together to monitor the algal bloom and updates will be provided on our website ( as we receive new information.

To learn more about blue-green algae visit the health unit website at, or call Health Connection weekdays from 8:30 a.m. to 4:30 p.m. at 705-721-7520 or 1-877-721-7520.

Two Muskoka lakes in Gravenhurst and Muskoka Lakes have been found to have blue-green algae blooms going in to Thanksgiving.