Public Service Announcement - Harmful Blue-Green Algae in Lake Nosbonsing

PUBLIC SERVICE ANNOUNCEMENT:  Harmful Blue-Green Algae in Lake Nosbonsing

Aug 21, 2026

LAKE NOSBONSING, ON - The North Bay Parry Sound District Health Unit (Health Unit) is advising residents to exercise caution after a potential blue green-algae bloom was reported to the Ministry of the Environment, Conservation and Parks (MECP) on August 20, 2026 in Lake Nosbonsing (near Astorville Bay and Perron Island Bay).

There is a risk that harmful toxins can be produced by blue-green algae. These toxins can stay in the water for up to three weeks after an algae bloom is gone, causing skin irritation, and if swallowed, diarrhea and vomiting.

Those who use the water of Lake Nosbonsing may be affected depending on their closeness to the algae bloom. Wind direction, water flow, and other environmental conditions that cannot be predicted or controlled, make it difficult to determine where and when the bloom is present.

Individuals who live near where a bloom was reported or where a bloom is visible should exercise their judgment before using the water and follow these safety measures:

• Avoid using the water for drinking, swimming, bathing or showering. Keep children and pets away from the bloom. Using a private water treatment system or boiling the water will not destroy the toxins. Private systems relying on lake water should use an alternate drinking water source, such as bottled water.
• Avoid swimming and other water sports where a bloom is present.
• Do not allow pets or livestock to swim in or drink the water.
• If skin contact does occur with a bloom, wash with soap and water, then rinse thoroughly with clean water to remove algae.
• Follow the Ministry of the Environment, Conservation and Parks Guide to Eating Ontario Fish. Exercise caution with respect to eating fish caught in water where blue-green algal blooms occur. Do not eat the liver, kidneys, or other organs of the fish.

For more information about harmful algae, visit myhealthunit.ca/algae or contact the Health Unit at 705-474-1400, Ext. 5400.

For further details on the sampling process, contact the Ministry of the Environment, Conservation and Parks Spills Action Centre at 1-800-268-6060.

Quick Facts

• Cyanobacteria – also called harmful algae, 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 in the water.
• The Health Unit asks municipalities to post appropriate signage at the lake’s public access points to allow the public to make educated decisions on their water activities.
• Climate change can create conditions that are more favourable to harmful algal blooms. Warmer air and water temperatures, more precipitation events, and droughts can all affect the growth and toxicity of algal blooms. Fertilizers and soaps that run off into the lake may also promote harmful algal blooms.
• Dense, harmful algae blooms may make the water look bluish green, like green pea soup, or turquoise paint. Very dense blooms may form solid-looking clumps.
• Fresh blooms often smell like newly mown grass, while older blooms may smell like rotting garbage.
• Blooms are not able to be removed from the water; however, they can come and go throughout the season.
• Even when a bloom has disappeared, toxins can survive in water bodies for a period of time.
• Long-term toxin exposure at high levels may cause liver and nervous system damage.

Media Inquiries:

Kylie Wurdell, Public Relations Specialist
P: 705-474-1400, ext. 5221 or 1-800-563-2808
E: communications@healthunit.ca