Algal blooms in border waters raise questions and concerns

Adam Heathcote has been studying blue-green algae blooms for over 15 years, including a lot of work in lakes in Iowa and southern Minnesota surrounded by farms and other development, where it’s common to see intense algal blooms.

But that didn’t bring him back to what he saw last month in Boundary Waters Canoe Wilderness, when paddling at Burnt and Smoke Lakes–two small lakes off Sobel Lake, a popular entry point into the BWCA region north of Toft, Minnesota.

A neon blue algae bloom was seen on Burnt Lake in the Boundary Waters Landboat Area last month.

Courtesy of Lynn Sethna

said Heathcote, director of the Division of Water and Climate Change at the St. Croix Institute for Station Watershed Research, part of the Minnesota Science Museum.

“I’ve never seen a bloom so much where it was like thick paint, neon blue, neon green, and lake level, and not only [in] A slightly isolated bay,” Heathcote described. “Two of the three lakes we sampled at Boundary Waters had this happening across nearly their entire surface area.”

Heathcote was surprised because these lakes are protected; They are surrounded by the wilderness.

There are algae in every lake. They are a healthy part of the ecosystem. It becomes a problem when algae are dominated by cyanobacteria, which can produce toxins that are harmful to humans and pets.

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Not all algal blooms are toxic. But Lienne Sethna, a postdoctoral fellow who works with Heathcote, said they examined the algae found in Boundary Waters under a microscope. They discovered three types of cyanobacteria that produce different types of toxins.

“It’s something that we’re really concerned about, and it’s something we really hope to address through this study,” Sethna said.

The purest lakes in Minnesota

Researchers study some of the cleanest and most pristine lakes in the state, just in and out of the wilderness. They’re trying to figure out why the algae’s situation has changed so unexpectedly. They have also documented cyanobacteria in Lakes Elbow and Finger, part of the Timber-Frear Canoe Trail in the Upper National Forest and on Lake Sawbill.

Paddle sitting in lake water next to blue neon algae

A neon blue algae bloom was seen on Burnt Lake in the Boundary Waters Landboat Area last month.

Courtesy of Adam Heathcote

Scientists measure nutrients, algae, water temperature and oxygen levels. They focused in part on Lakes Burnt and Smoke due to previous reports of algal blooms there.

Claire Shirley owns Sawbill Canoe Outfitters with her husband Dan. She said her family remembers seeing algae in those lakes since her grandparents started working in 1957.

Shirley said these lakes are shallow, with a muddy bottom and historically light fluffy fish catch that does not appear to have been affected by algae.

“No one has ever gotten sick or reported problems this way either,” Shirley said. “So it’s something we’ve kind of been living with for a very long time and have always been aware of. But we’re excited and grateful that someone has studied it. And we’d be really curious to hear what they’re going to find out.”

History in the sediment

Heathcote said there has been evidence of algal blooms in northern Minnesota’s shallow lakes since the 1700s. But he suspects the flowers in the area are becoming larger, more persistent, and more toxic.

To verify this, scientists extract samples from the sediment that gradually accumulates on the bottoms of the lake. Cyanobacteria create pigments that are preserved in sediments.

A person on a boat pulls a sample of sediment from a lake

Adam Heathcote pulls sediment cores from Eastern Twin Lake in the Upper National Forest.

Courtesy of Lynn Sethna

“We can look back through those layers, almost like reading the pages of a book,” Sethna explained.

“We use these layers to understand how nutrients and algae have changed over time. And so we use that to understand how cyanobacteria or harmful algal blooms occurred in the past and what kinds of factors have changed from historical conditions to the present day to help us understand why they happen now.”

Two possible reasons

Scientists have two hypotheses for what provokes flowering in these wild lakes.

First, climate change. Lakes are warmer. This allows the nutrients that have accumulated in the sediment to be more readily available to the algae at the top of the lake.

The second theory: dust. Researchers believe that nutrients are leached into the lakes from the atmosphere and help nourish these algae.

Heathcote admitted, “We had to pass the laughter test in this test first because of course you think, ‘What can dust do with these huge lakes?'” ”

But he said several influential studies have documented the effect of dust in remote alpine lakes in the foothills of the Rocky Mountains in Colorado.

Algae blooms along the shore of the lake

A bright green algal bloom appears along the shoreline of Smoke Lake in the border waters.

Courtesy of Lynn Sethna

For the first time in Minnesota, Heathcote and colleagues set up a network of dry sedimentation monitors to capture and measure nutrients falling from the sky.

Heathcote believes that it is likely that both global warming and atmospheric deposition are contributing to the growing trend of toxic cyanobacterial reproduction in northern Minnesota. This project seeks to confirm that.

While much research has been done on algal blooms in areas of obvious human influence, scientists are still working to understand the global drivers that fuel them.

“We don’t really know what we’re going to discover,” Heathcote said. “This is truly cutting-edge research. This is the first study of its kind in Minnesota and one of the first in the world.”

Anyone who sees a suspected harmful algal bloom in a remote northern Minnesota lake are asked to contact the researchers at or on Twitter @scwrs_mn

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