What is this smell? It could be blue-green algae – City of Mississauga

At this time of year, blue-green algae can become an unwanted guest during your visit to the lake, river, or waterfront park. Blue-green algae blooms appear in late summer and early fall and can be harmful to your health, the environment, and our local drinking water source. Knowing how to spot, prevent and report blue-green algae is important for your safety and the health of the environment.

What is blue-green algae?
blue-green algae are a type of bacteria that can occur naturally in ponds, lakes, and streams, causing the water to look often bluish green or sometimes olive green or red. It can also create a rotting smell. Although not normally visible in the water, when conditions are right, algae can form a large floating mass or layer (scum) called a bloom. These blooms most often occur in late summer and early fall, when the water is shallow, slow-moving, warm, and full of nutrients such as nitrogen and phosphorus. These nutrients can enter the water from fertilizers and contaminated runoff.

What to do if you see blue algae
While algae occur naturally and provide food and habitat for native species, blue-green algae can produce toxins that can be toxic to humans, animals, and aquatic wildlife. The toxins are spread by contact, digestion and inhalation and in humans this can lead to diarrhoea, nausea and respiratory problems. If you spot a blue-green algae bloom, assume toxins are present.

  • Check swimming and fishing advisories before visiting lakes and rivers. Avoid using, drinking, bathing, fishing or swimming in water where blue-green algae is present.
  • Watch for dead fish and other dead animals along the shore. If you see an abundance of dead fish along the shore, contact the Ministry of Natural Resources and Forestry. For questions about dead animal sightings in Mississauga, contact Animal Services at 905-896-5858.
  • Keep an eye on your pets – don’t let them drink or access water or ingest dead animals. Algae can also stick to your pet’s fur, which they may ingest when cleaning themselves.
  • Call Spill Action Center (1-800-268-6060) to report it.

The City of Mississauga is coordinating with Peel Public Health who monitor water quality at three of Mississauga’s beaches: Jack Darling Memorial Park, Lakefront Promenade and Richard’s Memorial Park. Signs are posted at these beaches if bacteria levels in the water are high enough to pose a health risk.

Example of signage along the Mississauga waterfront

Prevent blue algae
When debris and nutritious waste, such as animal waste and fertilizer, runs off your property and into your street catch basins, it ends up in our streams and rivers. These pollutants end up in Lake Ontario, Mississauga’s largest source of drinking water.

Reduce the risk of blue-green algae through prevention:

  • Use phosphate-free detergents and cleaners, and consider taking your car to a commercial car wash instead of washing it in your driveway. When you wash your car in your driveway, the soaps and detergents can flow into the rainwater catch basins on the roadway.
  • Apply any commercial fertilizer product strictly according to the manufacturer’s instructions and prevent excess fertilizer from spilling onto pavement or sidewalks where it can flow into stormwater catch basins.
  • Always pick up animal droppings and dispose of them properly. Pet waste contains high levels of nutrients, bacteria and viruses that make it a serious threat to water quality.

To learn more about the City’s stormwater system and how to prevent stormwater pollution, visit mississauga.ca/stormwater and follow @saugastormwater on Instagram.

Key words


Media Contact:
City of Mississauga Media Relations
[email protected]
905-615-3200 ext. 5232
TTY: 905-896-5151

About Shelly Evans

Check Also

Fossil Free Penn Camp returns to College Green, calling for divestment and action UC Townhomes

Fossil Free Penn at their camp on College Green on September 15, 2022. Credit: Ana …