The rise of blooms in local waters

While cyanobacteria are naturally present, there is an ongoing discussion regarding an increase in the frequency and intensity of blooms in Minnesota, according to Dr. Christopher Filstrup, applied limnologist and director of the Central Analytical Lab at the U of M Natural Resources Research Institute. Reports indicate that cyanobacteria blooms are appearing in lakes where they were not previously observed, including near the Lake Superior shoreline and certain forested lakes within the Boundary Waters Canoe Area Wilderness (BWCAW). 

Dr. Filstrup told Boreal Community Media that factors such as "warming temperatures, increased thermal stratification of the water column, more frequent severe weather events, and strengthening flood-drought cycles" are considered potential contributors to this trend. The exact reasons for increased blooms vary for each specific lake. 

Health and safety concerns

When cyanobacteria bloom, they can produce toxins that become a concern for anyone coming into contact with the affected water, including pets. "Often, dogs get sick after leaving the lake as they lick cyanobacteria cells off of their coats, although drinking from waters with toxins that attack the nervous system has a more immediate impact," Dr. Filstrup said. For humans, exposures can happen through intentional or accidental ingestion, consuming contaminated drinking water, or unintentional consumption during recreational activities in infected waters. Some toxins can also become aerosolized, leading to respiratory exposure. 

The Minnesota Department of Health (MDH), the Minnesota Pollution Control Agency (MPCA), and the Grand Portage Band of Lake Superior Chippewa may issue alerts if cyanobacteria toxin levels exceed recreational guidelines in specific areas. However, many blooms go unreported. Cook County Soil and Water Conservation District Manager and Watershed Planner Ilena Hansel shared that currently, Cook County does not have a system in place to alert people. "It is up to individuals and local groups to alert people to potentially toxic blooms in a body of water,"  she said. 

Another resource is BloomWatch, an app through the US Environmental Protection Agency, where users can report potential cyanobacteria blooms or see if a bloom has been reported on a particular lake. 

Dr. Filstrup recommends following the MPCA's guidelines of "When in doubt, stay out," to prevent accidental exposure. "If a water body looks like pea soup or has a dense green or blue-green surface scum, then it would be best to avoid it," he said. It is important to note that a bloom does not always need to be large or dense to pose a risk. Toxins can be present even in areas with little visible algae, or they can persist in the water after a bloom has decomposed or shifted due to wind.

Upcoming workshop

To provide community members with more information about cyanobacteria, a workshop led by Dr. Filstrup will be held on August 11, 2025, from 1:00 p.m. to 3:30 p.m. at the Grand Marais City Hall and Zoom. The workshop is open to everyone, regardless of whether they live on a lake. 

Workshop attendees will learn: 

• What cyanobacteria are and their role in lake ecosystems.

• Why they are problematic for both people, pets, and aquatic environments.

• How to identify a bloom and potential methods for testing for toxins.

• Ways individuals can help reduce the risk of cyanobacteria blooms in local lakes

• Simple do-it-yourself tests for identifying potentially toxic algae blooms.
  
  

Registration is recommended but not required. In-person space at City Hall is limited to 45 people. If participating via Zoom, visit: cookswcd.org.

For questions, contact Cook County SWCD at 218-387-3648.