The Grand River Conservation Authority (GRCA) is advising people not to fish or swim in Conestogo Lake.
The conservation authority issued the warning after what it believes to be a small blue-green algae bloom was observed in the lake reservoir.
"Hot summer days create the perfect conditions for algae to grow and bloom in large bodies of water," the conservation authority said. "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."
According to the conservation authority, some varieties of the algae can produce toxins that are harmful to both people and pets. As such, visitors to the Conestogo Lake Conservation Area are being told to avoid contact with the algae, not to eat fish from the lake or use the water for any purpose, and not to swim where the scum is observed. Kids and pets should be monitored to ensure they don't come into contact with the algae. While boating in the water is still permitted, recreational users should avoid touching the algae.
The Ministry of the Environment, Conservation and Parks and the Wellington-Dufferin-Guelph Public Health Unit have been notified about the suspected bloom, the conservation authority said.
A similar blue-green algae bloom was observed at Belwood Lake in late July. The algae has appeared at the two lakes in the past, as well as at Guelph Lake, and Woolwich reservoirs, and Snyder’s Flats. There is permanent signage at those locations to alert visitors to the potential for blue-green algae blooms and the need to take precautions.
"A new blue-green algal bloom often smells like fresh cut grass, while an older bloom can smell like rotting garbage," the conservation authority said.
Additional information about blue-green algae can be found on the GRCA website.