Suspected blue-green algae to impact swimming, fishing at Conestogo Lake
Posted Aug 12, 2025 06:12:55 AM.
Last Updated Aug 12, 2025 11:36:05 AM.
Those looking to cool off during the latest heat wave in Waterloo Region and beyond, don’t take a dip in Conestogo Lake.
The Grand River Conservation Authority (GRCA) said a suspected small blue-green algae bloom has been found at the lake reservoir.
“Hot summer days create the perfect conditions for algae to grow and bloom in large bodies of water,” reads a notice from the GRCA.
“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.”
The discovery could mean danger for swimmers and pets. The GRCA warns that blue-green algae can be toxic, and if you’re visiting the lake, avoid the water.
Don’t swim in it, don’t drink it, keep your pets out of it, and don’t eat any fish from it.
In years past, blue-green algae have been an issue at Conestogo Lake, as well as Belwood Lake, Guelph Lake, Woolwich reservoirs, and Snyder’s Flats.
Earlier in July, a small blue-green algae bloom was seen at Belwood Lake. The concerns around that bloom remain in effect.
“When an algal bloom starts to grow, a noticeable green or brown scum will form on the surface of water bodies, and the water will 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,” warns the GRCA.
A new bloom will give off a fresh cut grass smell, while an older bloom smells like rotting garbage.
More information on blue-green algae can be found here.
