Warning Issued Over Toxic Blue-Green Algae in Belwood Lake, Woolwich Reservoirs

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The Grand River Conservation Area has issued a warning regarding the presence of blue-green algae, also known as cyanobacteria, in Belwood Lake and Woolwich reservoirs. Both residents and visitors have been urged to keep children and pets well clear of the affected areas.

The caution extends to advise against contact with the bacteria-infested water and to abstain from consuming any fish from these water bodies. While no notice has been given prohibiting boating activities, a strong suggestion has been made to steer clear of the algae.


Particular regions within Belwood Lake, where visible green or brown algae scum can be noticed, have been declared unfit for swimming. Cyanobacteria share certain traits with algae, though it is imperative to note that they are fundamentally bacteria.

In large concentrations, some variants of this bacteria can produce toxins potent enough to induce sickness in both humans and animals. As a matter of fact, these cyanobacteria thrive on the nutrients they absorb from fields and lawns. These nutrients often find their way into surrounding water bodies and reservoirs due to heavy rainfall and spring thaws, resulting in a rapid multiplication of the bacteria, causing a surface bloom or scum formation.

Such infestations tend to primarily occur during periods of late summer or early autumn in regions where the water is warmer and the current is weaker. An algal bloom’s onset is generally marked by the formation of a discernible green or brown scum on the water surface, making it resemble a broth of green or bluish-green peas.

Upon a full bloom, the algae could appear as though paint has been spilled along the shoreline. A fresh algal bloom often gives off a fragrance similar to freshly-mown grass, while a bloom that has aged could emanate a foul odor akin to rotting garbage.