The blue-green algae that bloom in lakes and waterways produce a toxin that is harmful to humans — and this toxin, microcystin, is present in lakes in every Canadian province, a new study has found.

Blue-green algae, or cyanobacteria, can kill fish, increase the cost of water treatment and devalue shoreline properties. The algae also produce microcystin, a known potent liver toxin to humans and mammals that is classified as a possible human carcinogen.

Researchers at universities across the country looked at the prevalence of microcystin in 246 bodies of water for a paper published in the Canadian Journal of Fisheries and Aquatic Sciences. All regions in Canada were found to contain lakes that have high levels of microcystin, though nutrient-rich lakes and reservoirs in central Alberta and southwestern Manitoba were found to have the highest toxin concentrations.

"Canadians enjoying their summer at the cottage need to know that those green scums of algae washing up on their beach are not only unsightly, but can also be a threat to their health and their children's health," lead author Diane Orihel said in a release. "It's time to get serious about cleaning up the nutrients polluting our lakes."

The study authors suggest that further research, including whole-ecosystem experiments to determine how changing nutrient inputs to lakes affect microcystins, is necessary for governments to work out effective management strategies to improve water quality in affected lakes.