Blue-green algae is unusual on Lake Superior but experts say that might not last

Lake Superior is known for its cool, blue beauty, but the largest freshwater lake in the world (by surface area) has a new antagonist: blue-green algae.

The most recent bloom confirmed in the Thunder Bay District by the Ministry of Environment, Conservation and Parks (MECP) was reported on Lake Superior at Shuniah's Birch Beach on July 28.

Before this, the last bloom on Lake Superior was confirmed by the ministry in 2021 in Black Bay. However, the ministry said blue-green algal blooms have been reported by U.S. authorities along the southwest shoreline as early as 2012.

Blue-green algae blooms aren't common on Lake Superior, but experts say warming temperatures may make them more frequent.

"It is a new thing," said Azim Mallik, chair of the biology department at Lakehead University in Thunder Bay. 

Blooms are usually seen in late summer or early fall, according to the MECP. Typically, Mallik said harmful algal blooms happen in warmer, shallow water, whereas Lake Superior is large, deep and cold.

"This report indicates that the environment has changed, water temperature or other chemical properties of [the] water has changed and as a result of that, this cyanobacteria population increased," Mallik said.

Environmental conditions such as light availability, warmer water, invasive species, calmer water flow and nutrient loading – meaning too much nitrogen and phosphorus – can all cause cyanobacteria to flourish.

"In my view it is not quite too alarming, but it is not very surprising either, because we know that global warming is increasing air temperature and water temperature," he said.

People, pets at risk of health problems 

The Thunder Bay District Health Unit (TBDHU) has tracked 23 blue-green algae blooms from 2019 to July 28, 2023. Besides the bloom on Lake Superior, the district has seen three other blooms this summer on inland lakes.

"It is quite unusual," said Matt Bradica, public health inspector with the TBDHU, of the recent Lake Superior bloom.

Blue-green algae produces toxins, which, when ingested, can make people and pets sick, he said. He advises people to watch for:

• Fever
• Headache
• Vomiting
• Diarrhea
• Skin and eye irritation and rashes

Prolonged ingestion can also lead to liver damage, he said.

"When there is blue-green algae present, it is important to avoid drinking, swimming, bathing, even brushing your teeth with the contaminated water," Bradica said. "Pets as well are extremely vulnerable to the blue-green algae toxins … there have been a number of pet deaths associated with it."

People are encouraged to wipe themselves off if they have come into contact with blue-green algae, and to see a health-care provider if they experience any immediate health concerns. 

Prevention comes down to land management practices

Mallik, the health unit and MECP all pinpoint climate change as contributing to rising cases of blue-green algae. 

"People shouldn't [be alarmed] but they can expect these types of algal blooms in the future more frequently," Mallik said.

"The land management practice should be adapting to this changing environment, changing climate, and so the people who are managing our landscape should be mindful of what goes in the lake, particularly in the shallower part of the lake so that this type of cyanobacterial bloom doesn't happen," he said.

One key action item is preventing household and agricultural waste from seeping into waterways, which is what causes nutrient loading, he said. 

A spokesperson for the MECP also provided CBC News with a list of preventive steps people can take:

• Using phosphate-free detergents
• Not bathing in lakes
• Maintaining a naturalized shoreline on lakefront properties, and not using fertilizers
• Reducing nutrient run-off by increasing upland infiltration, and populating shorelines with native plants
• Making sure septic systems do not leak or discharge into water bodies

The ministry has a 12-point action plan to address blue-green algal blooms and works with municipalities, local medical officers of health and other partners to track and address blooms affecting Ontario's lakes and rivers, MECP spokesperson Gary Wheeler said in an emailed statement to CBC News.

People can report a suspected blue-green algae bloom to the Spills Action Centre at 1-800-268-6060.