Harmful algae blooms subside on Cedar, Isles

Lake of the Isles. File photo

Harmful algae blooms that have made Cedar Lake and Lake of the Isles toxic to people and animals and turned the water murky and brown have begun to clear with warming weather, parks officials believe. 

The blue-green algae bloom, first reported on Cedar Lake in mid-May and later found on Lake of the Isles and Lake Nokomis, is subsiding. The Minneapolis Park and Recreation Board’s water quality staff have observed a fading of brown spots on the lake and improvements in water clarity based on measurements taken at Cedar Lake and Lake of the Isles, according to a press release. 

The MPRB is removing signs from around the lakes warning people to avoid the water this week. 

The harmful algae bloom (HAB) produces cyanotoxins that can cause illness in humans and animals. The Minnesota Department of Health is investigating the death of a large breed dog that drank from Cedar Lake on May 12. 

The MPRB believes the blue-green blooms in city lakes were related to a rapid ice-out this spring. Plankton samples collected last winter showed the algae blooms at the three lakes started under the ice. When a rapid ice-out was followed by a cooler spring, conditions allowed for algae to persist, the Park Board said. Typically, the naturally occurring phenomena is more common in late summer with higher temperatures.