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Green algae floating on the surface of lake or pond water. (Image Credit: Constantin Opris/Dreamstime)
Cyanobacteria Advisory

Blue-green algae AHS health advisory issued for Reesor Lake

Aug 5, 2026 | 1:07 PM

A cyanobacteria advisory is in effect for Reesor Lake at Cypress Hills Provincial Park after blue-green algae was identified in the water.

Visitors are being advised not to swim or wade in areas where cyanobacterial blooms are visible, and to avoid contact with blooms in the water or washed up along the shoreline.

The advisory also warns people not to drink or cook with water from the lake, noting that boiling the water will not remove toxins produced by cyanobacteria.

Officials say an alternate source of drinking water should also be provided for pets and livestock while the advisory remains active.

People are also being reminded not to eat whole fish or fish trimmings from the lake, as toxins can collect in fish organs. Fish fillets contain fewer toxins and are considered safer to eat.

Cyanobacteria are naturally occurring, but larger blooms are more common during warm weather.

The blooms can appear blue-green, greenish-brown, brown, pink or red, and may look like scum, streaks, grass clippings or pea soup. They can also produce a musty or grassy smell.

Exposure to cyanobacteria can cause skin irritation, rash, sore throat, red or swollen eyes, nausea, vomiting and diarrhea.

Symptoms can appear within one to three hours after contact or ingestion, and children can experience more severe symptoms, with pets also at risk of illness or death if exposed to cyanobacteria.

Weather and wind conditions can move blooms around the lake, so the advisory will remain in place for Reesor Lake until further notice.

Officials said areas of the lake where cyanobacterial blooms are not visible can still be used for recreational purposes while the advisory is active.

Anyone with concerns about possible cyanobacteria exposure can contact Health Link by calling 811.

Multiple locations across Alberta are under the same advisory, and can be viewed on the Alberta Health Services website.