It's a hot summer and that means blue-green algae is back, GRCA warns

Yahoo

26-07-2025

The hot weather this summer means blue-green algae is starting to bloom in local waterways, the Grand River Conservation Authority says.
So far this summer, blue-green algae has been seen near the west side of Shand Dam at Belwood Lake reservoir.
In the past, the algae has also shown up in Conestogo Lake, Guelph Lake and Woolwich reservoirs, as well as at Snyder's Flats.
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," the conservation authority says.
"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."
The algae grows thanks in part to nutrients from fields and lawns that end up in local waterways and reservoirs when it rains, the authority says.
People are reminded not to touch the algae as it can be harmful to people and pets.
As well as avoiding any contact with the blue-green algae, people shouldn't use water from a reservoir where the algae is found and should not eat fish from the water, either.
Assume it contains toxins: health unit
Wellington-Dufferin-Guelph Public Health notes on its website that blue-green algae, also called cyanobacteria, usually shows up in late summer or early fall and higher water temperatures help it grow.
"There's no way to tell by looking at a bloom whether it contains toxins or not. As a precaution, regard any blue-green algal bloom as potentially toxic," the health unit says.
People who do come in contact with blue-green algae may experience itchy or irritated eyes and skin, headaches, fever, diarrhea, stomach pain and nausea. If large amounts are ingested, there can be more serious effects such as liver damage.
The health unit also notes infants and children under the age of six are most at risk of developing health problems if exposed to the algae.
If someone does come into contact with blue-green algae, Wellington-Dufferin-Guelph Public Health says they should rinse off immediately with clean water and watch for symptoms. If symptoms show up, speak to a health-care provider.
People who spot blue-green algae where there are no posted signs are asked to report it to the Grand River Conservation Authority and or the Ministry of Environment, Conservation and Parks spill action centre.