Lake Superior summer: Harmful algal blooms come to a lake once believed immune
On a calm morning in late summer 2019, Jim Bailey was kayaking on Lake Superior near Thunder Bay, Ontario, when he found himself paddling through thick green scum, the likes of which he’d never seen in those waters. Puzzled, he headed into the open bay where he could see green patches stretching out about three kilometers.
Bailey – recently retired as coordinator of the local Remedial Action Plan Office – had his suspicions about what he was seeing. It had been his job to oversee a government office tasked with identifying and controlling local sources of pollution. He emptied his water bottle, scooped up some scum and headed for shore. Ten minutes after handing his sample to Lakehead University for analysis, his suspicions were confirmed: It was cyanobacteria, capable of producing toxins harmful to people and wildlife.
“I’ve lived on the lake my entire life, and I’d never seen algae before,” said Bailey. “I knew if it was algae, it would be a landmark and not a good one.”
The incident was the first documented case of a cyanobacteria bloom along Lake Superior’s northern shore in Canada. The previous summer had seen reports of a massive bloom of cyanobacteria – also known as blue-green algae – on the southern side of the lake in the United States.
“The 2018 bloom was the largest ever recorded on the lake,” said Robert Sterner, director of the Large Lakes Observatory at the University of Minnesota Duluth. “One hundred kilometers of shoreline turned opaque green. It was quite extraordinary.”
As the deepest and most northern of the Great Lakes, Superior was once thought immune to cyanobacteria blooms. It was considered largely devoid of growth-promoting nutrient runoff from surrounding land. But more importantly, it was just too cold, even in summer.
Today, Superior is one of the fastest warming lakes in the world, said Sterner.
Still, it was a shock when the first report of cyanobacteria came in 2012, on the shoreline in Wisconsin near the Apostle Islands. There have been several minor blooms since then, the biggest one happening in 2018. This year, a mild winter and hot start to the summer means Superior’s waters are warmer than normal, possibly setting the stage for another substantial bloom.
Jury out on toxins
Most people think of Lake Erie when they think of algal blooms. With its warm, shallow waters and the phosphorous runoff from surrounding agricultural land, Erie has long been the poster child for harmful algal blooms. In 2014, Toledo, Ohio, was forced to shut down its water supply after toxic cyanobacteria blooms formed over the city’s water-intake pipe.
Cyanobacteria can produce several serious toxins, causing hay fever-like symptoms, skin rashes, respiratory and gastrointestinal problems. Pets and livestock have died after swimming in or drinking contaminated water, but there have been no human deaths.
So far, none of the blooms sampled from Superior have produced enough toxins to pose a danger. But as aquatic ecologist Brenda Moraska Lafrancois cautions, sample sizes have been too small to rule out the possibility. Plus, the list of toxins tested has been short, and cyanobacteria produce many toxins for which no health standard has been established.
“This whole issue of whether these blooms are toxic is still an open question,” said Moraska Lafrancois, who works in Ashland, Wisconsin, for the Midwest region of the National Park Service.
Nathan Wilson agrees. He is a PhD student in environmental biotechnology at Lakehead University in Thunder Bay, Ontario, and was the one to confirm Bailey’s sample was cyanobacteria.
“We don’t know much about when it does and doesn’t produce toxins,” said Wilson. “People are working on that.”
But blooms don’t have to produce toxins to wreak havoc. They can clog intake screens at water treatment plants and affect water’s taste and smell. When large blooms die off, bacteria in the water use up oxygen to break down the blooms, making it hard for fish and other aquatic life to survive.
Cyanobacteria have been known to be part of North America’s ecosystem for centuries. In the 1700s, Scottish explorer Alexander MacKenzie noted a bloom in Lake of the Woods, which straddles present-day Ontario, Manitoba and Minnesota.
Cyanobacteria are particularly hardy and, given the right conditions, can outcompete other types of non-toxin-producing algae. They contain tiny sacks of gas that give them buoyancy so they can float up and sink down, accessing nutrients throughout the water column. They also have thick cell walls that allow them to survive better in winter than some forms of algae.
But the scientific consensus is that climate change is giving cyanobacteria a more pronounced advantage, leading to more intense, widespread blooms. It’s not just that climate change is causing Superior’s waters to warm at an unprecedented rate, but that it’s led to more intense rainstorms in the Great Lakes region.
The western region of Lake Superior has seen increases in precipitation intensity of around 35-40% since the mid-1900s. These heavy rains wash loads of sediment and nutrients directly into the lake and into surrounding rivers that lead into the lake, providing a banquet for cyanobacteria.
As Sterner points out, the largest blooms happened in 2012 and 2018.
“2012 is the infamous year when the rainstorm tore out a lot of infrastructure in Duluth and 2018 was also a large rain event,” he said.
But while warming waters and heavy rainfalls are part of the equation, there may be more going on than meets the eye.
“It’s an evolving story,” said Sterner. “The science is just starting to fall into place.”
What’s up with Chequamegon Bay?
For example, researchers are still trying to puzzle out the mystery of Chequamegon Bay near Ashland, Wisconsin.
Relative to the rest of Lake Superior, its waters are shallow, warm and still. Plus, it’s surrounded by various sources of phosphorous from nearby communities – conditions consistent with blooms in Lake Erie.
And yet, researchers have not seen a single bloom in the bay.
“If Lake Superior is experiencing more blooms, why haven’t they started in Chequamegon Bay?” asked Matthew Cooper, an aquatic ecologist and affiliate faculty with Northland College’s Mary Griggs Burke Center for Freshwater Innovation in Ashland, Wisconsin.
He and his colleague Matt Hudson are working on answers to this and many related questions: “So we’re not seeing blooms, but are we at a tipping point? Can we take some bay water, mess with it and make it bloom? And can it teach us about what might happen in the future?”
In 2019, Cooper and Hudson collected water samples from all around the bay and brought them back to the lab. They did indeed detect low levels of cyanobacteria and were able to get them to grow by feeding them phosphorous and warming the water.
“But we didn’t turn the beakers pea-soup green, like we thought we might,” said Cooper.
The pair had hoped to continue their work last summer, but pandemic restrictions forced them to postpone until this year. They are looking into several possible explanations, including that the bay is home to a different species of cyanobacteria than the rest of the lake. Another possibility is that the bay’s phosphorous may not be the kind that cyanobacteria can use, or that the bay has cloudier waters than the rest of the lake, which would mean less light reaching the bacteria for photosynthesis.
Meanwhile, the frustration for residents and researchers alike is that not much can be done locally to control the global phenomenon of climate change. It’s possible to make shorelines less prone to erosion and hence soil less prone to sending nutrients into the lake. It’s also possible to reduce phosphorous leaks from sewage and agriculture. Some local governments around Lake Superior have implemented these strategies, but it’s still unclear how much of a difference they will make.
While algal and cyanobacteria blooms may affect Superior’s recreation and tourism-based economy, there is something less tangible but more significant at stake: the psyche of people who live around the lake.
“The blooms made The New York Times,” said Cooper. “Maybe it only affects a few swimming bays, but the perception is a big deal to a community that depends on Lake Superior being clean, clear and beautiful.”
The Great Lakes News Collaborative includes Bridge Michigan; Circle of Blue; Great Lakes Now at Detroit Public Television; and Michigan Radio, Michigan’s NPR News Leader; who work together to bring audiences news and information about the impact of climate change, pollution, and aging infrastructure on the Great Lakes and drinking water. This independent journalism is supported by the Charles Stewart Mott Foundation.