Update: Blue-green algae and GRCA reservoirs

The presence of a suspected blue-green algae bloom has been observed at the beach at Conestogo Lake Conservation Area. The Ministry of the Environment, Conservation and Parks (MECP) and the Wellington-Dufferin-Guelph (WDG) Public Health Unit have been notified.

The GRCA consulted with WDG Public Health who has recommended a beach closure due to the observation of blue-green algae. The GRCA has made the decision to close the beach at Conestogo Lake Conservation Area for the remainder of the season due to a combination of factors.

The water levels in the Conestogo Lake reservoir are already lower than normal for this time of year as a result of the Conestogo Dam rehabilitation project. The construction project has required the water in the reservoir to be drawn down gradually to allow the contractor access and time to complete repairs of the dam. As a result, the West (shorter) boat launch at Conestogo Lake Conservation Area will be out of service for the remainder of the season beginning Saturday, August 23, 2025, as communicated in a news release earlier today. The rate of draw down will increase following Labour Day, September 1, 2025, resulting in the closure of the second boat launch shortly afterwards.

“We know that blue-green algae conditions can change very quickly due to prolonged hot temperatures, wind direction, water flow and levels,” says Cameron Irvine, GRCA Supervisor of Water Quality. “The low water levels in the reservoir in combination with warm air temperatures create the perfect conditions for algae to grow and bloom in large bodies of water.”

Beach closures are rare at Grand River Conservation Areas. However, with the end of summer just weeks away, the decision to close the beach in this case is due to the combination of the suspected blue-green algae bloom impacting the beach and swimming area, as well as the anticipated further reduction in water levels, which will result in the closure of both boat launches.

The Conestogo Lake Conservation Area beach is now closed, and swimming is not recommended. Conestogo Lake Conservation Area visitors, recreational users and cottagers should implement the following additional safety measures:

• Keep children and pets away from the algae.
• Avoid contact with the algae.
• Don’t eat fish from the lake.
• Don’t use the water for drinking or any other purpose.
• Boating is currently allowed, but boaters and recreational users should avoid touching the algae.

Anyone with health-related questions may contact the Wellington-Dufferin-Guelph Health Unit.

More Information

The presence of a small blue-green algae bloom near the Conestogo Dam had been observed and communicated on August 11, 2025. The previous notice of a small blue-green algae bloom observed at Belwood Lake in late July, 2025, remains in effect.

Historically, blue-green algae blooms have occurred at the Grand River Conservation Authority’s Belwood Lake, Conestogo Lake, Guelph Lake and Woolwich reservoirs, as well as at Snyder’s Flats. There is permanent signage at these locations advising visitors of the potential for blue-green algae blooms and precautions that should be taken.

Anyone with health-related questions may contact the Wellington-Dufferin-Guelph Health Unit.

Blue-green algae thrive on nutrients from fields and lawns that find their way into local waterways and reservoirs during heavy rainfall and spring melts and cause their populations to grow rapidly, forming blooms or scum on the surface of the water. Some varieties of blue-green algae can produce toxins that are harmful to both people and pets.

When an algal bloom starts to grow, a noticeable green or brown scum will form on the surface of water bodies and the water look like green or bluish-green pea soup. Once blue-green algae are in full bloom, it may look like spilled ‘paint’ along the shoreline. A new blue-green algal bloom often smells like fresh cut grass, while an older bloom can smell like rotting garbage.

Visit the GRCA website to learn more about blue-green algae on GRCA reservoirs. The MECP Parks website provides additional information about blue-green algae.

-30-

Media contacts:

Lisa Stocco, GRCA Director of Strategic Communications and Environmental Education
Phone 519-621-2763 x2316  |  Email lstocco@grandriver.ca

Serena Catania, GRCA Supervisor of Communications and Marketing
Phone (519) 621-2763 x2240  |  Email scatania@grandriver.ca