Blue-green bloom lifted on MacLean Lake

Severn received notice on November 24 that based on test results from the Ministry of the Environment, Conservation, and Parks (MECP), the algae bloom initially identified on August 14, 2023, in MacLean Lake, Township of Severn has dissipated. Please contact the Simcoe Muskoka District Health Unit with any questions.

Blue-green algae bloom confirmed at Maclean Lake dock and boat launch

The Simcoe Muskoka District Health Unit (SMDHU) is informing residents and visitors to the Township of Severn that laboratory analysis has confirmed the presence of a blue-green algae bloom impacting Maclean Lake. The sample was taken from the Maclean Lake dock and boat launch located at 1914 Henry's Landing

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 when exposed in large amounts. Due to the confirmed presence of the bloom, the SMDHU are asking residents and visitors to exercise caution and recognize that toxins may also be present.

Safety measures as recommended by the SMDHU

As a precautionary measure, the SMDHU urges residents and businesses to avoid drawing or drinking water from private water supplies that are impacted by the lake where blue-green algae has been identified and to take the following precautions:

  • do not use a private water supply that is impacted or draws water from this area of the lake 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
  • fish taken from waters with cyanobacterial blooms have the potential to contain toxins
  • exercise caution when 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 water sport activities where an algae bloom is visible

The SMDHU strongly recommends seeking medical attention if symptoms such as skin, eye or throat irritation, allergic reactions or breathing difficulties occur following contact with the blue-green algae bloom.

Anyone who comes into contact with blue-green algae should wash with soap and water or rinse thoroughly with clean water. Swimming, bathing, or showering with water not visibly affected by a blue-green algae bloom is not expected to cause health effects.

Updates to be provided by the SMDHU

The SMDHU and the Ministry of Environment, Conservation and Parks will continue to work together to monitor the algal bloom and updates will be provided on both Severn's and the health unit's website

For further information, call Health Connection Monday to Friday 8:30 a.m. to 4:30 p.m. at 1-877-721-7520.

Links to general information and updates about blue-green algae are available on the health unit website at 


Simcoe Muskoka District Health Unit
Phone: 1-877-721-7520

Email to Township of Severn, August 14, 2023.