Cyanobacteria identified at Reesor Lake in Cypress Hills Provincial Park

By ANNA SMITH Local Journalism Initiative on July 24, 2025.

asmith@medicinehatnews.com

Blue-green algae, known as cyanobacteria, has been identified within Reesor Lake at Cypress Hills Provincial Park.

Cyanobacteria may be visible when weather conditions are calm, appearing as blue-green, greenish-brown, brown and/or pinkish-red “fuzz” on the surface of the water.

While it is natural, it does contain toxins which cannot be removed by boiling.

Visitors and residents are reminded to never drink or cook with untreated water directly from any recreational body of water, including Reesor Lake, at any time.

Those who come into contact with cyanobacteria, or ingest it, may experience skin irritation, rash, sore throat, sore red eyes, swollen lips, fever, nausea and vomiting or diarrhea. These symptoms generally appear within one to three hours after contact.

Anyone who makes contact with cyanobacteria is advised to rinse the area with tap water as soon as possible and to not swim or wade where the bloom is visible. Pets and children should also not be permitted to swim or wade in these areas.

As fish can carry these toxins in their livers, whole fish and fish trimmings from the affected areas should not be consumed by people or pets, though fish fillets are safe to eat.

Exposure to the bacteria may be fatal to pets.

Weather and wind conditions can cause algae blooms to move from one location in the lake to another, prompting this advisory to remain in effect for Reesor Lake until further notice. Areas of the lake where there is no visible bloom can still be used for recreational purposes, even while this Health Advisory is in place.

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