Harmful algae bloom on Cedar Lake, Lake of the Isles

Park officials are warning residents to stay out of Cedar Lake due to a harmful algae bloom that can cause illness. File photo

Officials are warning residents of a harmful algae bloom in Cedar Lake and Lake of the Isles and investigating if the natural phenomena caused a dog’s death.

The Minneapolis Park and Recreation Board is advising residents to stay out of Cedar Lake and Lake of the Isles, where a blue-green algae bloom is believed to have developed. The harmful algae bloom (HAB) produces cyanotoxins that can cause illness in humans and animals.

The Minnesota Department of Health (MDH) is investigating the death of a dog that drank from Cedar Lake on May 12, according to MPRB spokesperson Robin Smothers. Dogs are generally banned from swimming in Minneapolis lakes, but officials are reemphasizing the safety risk for animals in Cedar Lake during the HAB.

The dog was a large-breed adult that drank an unknown amount of water from the lake, according to an MDH spokesperson. Each year, the state sees a handful of cases of dogs dying due to harmful algae blooms.

The state has not received any reports on human illness related to the bloom.

On May 22, the MPBR reported a blue-green algae bloom is also present on Lake of the Isles and Lake Nokomis and similarly advised people to take caution near the lakes.

Blue-green algae are not, in fact, algae but a bacteria known as cyanobacteria that is commonly found in lakes, according to the MDH. Under the right conditions, the bacteria grows fast and forms blooms which can become dense, greenish scums that produce an unpleasant smell. People and animals who come in contact with or swallow impacted water can develop symptoms such as vomiting, diarrhea, sore throat, headaches and eye irritation.

The MPRB began warning people of the HAB on May 15 and started installing signage around the lakes the week of May 18.

Blue-green algae blooms occur naturally but typically come later in the summer, according to the MDH. Warm, calm waters are ideal conditions for the algae blooms, but the phenomena can occur at other times of year under the right conditions. The University of Minnesota lists urban and agricultural runoff and climate change as other contributing factors that can lead to such blooms. The blooms can also contribute to fish kills. Occurrences of blue-green algae blooms are on the rise in Minnesota, according to the U of M.

The MPRB believes the blue-green blooms in city lakes are 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. Officials believe the conditions will diminish as temperatures rise.

This is the first blue-green algae bloom to develop to the point of scum-forming on Cedar Lake, Smothers said. Other Minneapolis lakes have experienced such HABs, most recently Powderhorn Lake in 2019.

Water quality personnel in the MPRB are awaiting test results from a lab to officially confirm the blue-green algae bloom at Cedar Lake. The blooms will likely stay in place until conditions change. Officials recommend staying out of the lake until the water clears.

On a cloudy Thursday in May, kayakers and paddleboarders continued to push their way across the murky waters of Cedar Lake. At Hidden Beach, on the lake’s east side, a mother warned her children to stay out of the water. People hammocked and picnicked near the water while a group of jazz musicians jammed in the woods.

Cedar Lake has a more remote, wilderness feel than the rest of the Chain of Lakes, but that historically hasn’t meant it has higher water quality on average. The northern portion of the Chain of Lakes — Brownie Lake, Cedar Lake and Lake of the Isles — consistently score lower than Bde Maka Ska and Lake Harriet on water quality reports. Cedar Lake received a “C” on the most recent Minnehaha Watershed District’s Lake Grades Report in 2017, though it historically has averaged a “B” grade.

Keith Prussing, the longtime president of the Cedar Lake Park Association, said avid lake appreciators could see a difference in water clarity as soon as ice-out began in the early spring, with people first noticing a film-like substance on the surface near the west side of the lake. The health of the lake peaked in the mid-’90s, Prussing said, but has been declining more rapidly in the past three years. But no past issues have compared with the scale of this year’s blue-green algae bloom.

“There’s never been anything remotely at this scale,” Prussing said.

The Park Board does not believe the Southwest Light Rail Transit project construction is a contributing factor, Smothers said. Leaders of the Cedar-Isles-Dean neighborhood organization had wondered if construction work on the project may have caused the bloom.

Right now, the knowledge of the bloom is too vague to say why Cedar Lake is experiencing the algae bloom, Prussing said. Given the interdependent nature of the ecosystem, he wouldn’t be surprised if the SWLRT project, which has been doing work in the channel between Cedar Lake and Lake of the Isles, has had an impact.

“Coincidence does not equal causation; that being said, it does give one pause,” Prussing said.

He is hopeful the event will get locals thinking about how to make the lake healthier.

“This event has started a robust conversation about water quality,” Prussing said.

Prussing is also a member of the newly formed Cedar-Isles Master Plan Community Action Committee, a new planning effort by the MPRB that will seek to shape the future of the northern portion of the Chain of Lakes. How to improve water quality is likely to be a focus point once the CAC starts to meet in earnest this fall.