MACTIER Residents and visitors around two area lakes are being cautioned about confirmed cases of blue-green algae bloom.

Simcoe Muskoka District Health Unit issued warnings this afternoon, Friday Oct. 16, for those around the northwest end of MacTier’s Stewart Lake, in Georgian Bay Township; and in Severn Township at the north end of Otter Lake.

Public health urges caution where it is visible suggests these 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
  • avoid swimming and other water sport activities where an algae bloom is visible

They say 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 their website

And to learn more about blue-green algae visit the health unit’s 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.

An algae bloom has been spotted in the northwest end of Stewart Lake in MacTier, where the health unit is warning residents and visitors to be cautious about as of today, Oct. 16.