Green algae floating on the surface of lake or pond water. Constantin Opris/Dreamstime

By Jesse Gill

ADVISORY

Blue-green algae health advisory for Reesor Lake

Jul 23, 2025 | 8:51 AM

Alberta Health Services announced Tuesday, July 22 that Cyanobacteria (blue-green algae) has been identified on the waters of Reesor Lake at Cypress Hills Provincial Park.

Visitors to the lake are advised by AHS to take several precautions.

• Avoid all contact with cyanobacterial blooms. If contact occurs, wash with tap water as soon as possible.
• Do not swim or wade or all your pets to swim or wade in any areas where cyanobacteria is visible.
• Do not feed whole fish or fish trimmings from this lake to you pets.
• Consider limiting human consumption of whole fish and fish trimmings from this lake, as it is known that fish may store toxins in their liver. However, people can safely consume fish fillets from this lake.

Additionally AHS said visitors are reminded to never drink or cook with untreated water, including Reesor Lake, at any time.

Boiling of untreated water will not remove the toxins produced by cyanobacteria.

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An alternate drinking waters source should also be provided for pets and livestock during this advisory, according to an AHS news release.

Cyanobacteria is naturally occurring and often becomes visible when weather conditions are calm.

Appearing like scum, grass clippings, fuzz or globs on the surface of water, cyanobacteria can be blue-green, greenish-brown, brown and/or pinkish-red, and often smell musty or grassy.

People who come in contact with visible cyanobacteria or who ingest water containing cyanobacteria may experience skin irritation, rash, sore throat, sore red eyes, swollen lips, fever, nausea and vomiting and/or diarrhea, according to AHS.

Symptoms usually appear within one to three hours and resolve in one to two days.

Symptoms in children are often more pronounced; however, all humans are at risk of these symptoms.

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.

AHS said the advisory will remain in effect for Reesor Lake until further notice. However, the waters in which the cyanobacterial bloom is not visible can still be used for recreational purposes, even while the health advisory is in place.

For further information a person can call Health Link at 811 or visit www.ahs.ca/bga.