Chances are high that you saw it over the summer at your favourite lake: thick scum on the water’s surface, often resembling pea soup. Blue-green algae (also called cyanobacteria) can render water unsafe for swimming and often makes people, pets, livestock, and wildlife sick. In July, Nova Scotia listed 26 waterways suspected to have blue-green algae blooms. Officials with Alberta Health Services identified blue-green algae in areas of Camp Lake, east of Edmonton, and Haunted Lake (an ironic name for a place fouled by the sinister sludge), east of Red Deer. The Saskatchewan Health Authority issued a blue-green algae warning for Little Manitou Lake, southeast of Saskatoon. British Columbia’s Capital Regional District saw toxic algae blooms in three different lakes across two regional parks in August.