The Health Unit advises that a bloom of toxin producing blue-green algae has been detected on Whalley Lake in the Municipality of Magnetawan. Residents and visitors near this area need to take the following precautions:

  • If you use a private water system, do not use water from the lake for drinking, cooking and bathing. Boiling the water or using home water treatment devices will NOT destroy the toxins.
  • Avoid swimming or other water sport activities that could increase the risk of algae material and toxins contacting your skin or being swallowed.
  • Do not allow pets or livestock to swim in the water or drink the water.
  • Some toxins produced by cyanobacteria accumulate in the tissues of fish and shellfish, particularly in the guts including the liver, kidney, etc. We do not know if the toxins accumulated in fish would be a concern. It depends on how much you eat and how severe the cyanobacteria bloom. Be careful if you eat fish caught in water where cyanobacteria blooms occur. Do not eat the liver, kidneys and other organs of fish caught. Do not cut the organs when filleting.

These precautions are effective immediately. While the blue-green algae may not show the presence of toxins, there is always the risk that toxins could be produced. These toxins may stay in the water for up to three weeks after the algae bloom is gone.
The Health Unit and the District Office of the Ministry of the Environment and Climate Change cannot tell after blue-green algae blooms have been detected when the water is safe to use for private water systems.
You can find out more about blue-green algae, at or call the Health Unit at 705-474-1400, ext. 2400 or 1-800-563-2808.
Quick Facts

  • Cyanobacteria, also called blue-green algae or ‘pond scum’, are not really algae, but tiny bacteria.
  • Although usually hard to see, during hot weather they can grow rapidly to form a large mass, called a bloom. Blooms continually change and are difficult to predict. Wind, temperature or sunlight could change where the bloom is located in the water.
  • Even when a bloom has disappeared, toxins can persist in water bodies for a long time. Toxins can irritate the skin and, if ingested, cause diarrhea and vomiting. At high enough levels, the toxins may cause liver and nervous system damage.
  • If skin contact does occur, wash with soap and water or rinse thoroughly with clean water to remove algae.


Official Releases

pdfCyanobacteria_Frequently_Asked_Questions-rev.pdf552.14 KB

pdfNotice_to_Residents_-_BGA_Whalley_Lake.pdf155.57 KB

Media Inquiries Only
John Mitchell, Acting Communications Coordinator P: 705-474-1400, ext. 2221 or 1-800-563-2808 E:


pdf• Blue-green algae: information for cottagers and homeowners (2005, Ministry of the Environment and Climate Change)87.84 KB

pdf• Blue-green algae (cyanobacteria): a guide (2015, Water Resources Australia)1.84 MB

pdf• Blue-green algae presentation, Tuesday July 26, 2016 (2016, North Bay Parry Sound District Health Unit)1.08 MB