Discover How Polluted Lake Superior Really Is

Fall foliage along the North Shore of Lake Superior in Northern Minnesota

Written by Crystal

Published: July 31, 2023

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The Great Lakes hold a third of the world’s surface freshwater. Covering a massive 31,700 square miles, Lake Superior is the largest freshwater body in the world by surface area. It holds 10% of the world’s fresh water. But these lakes aren’t just massive bodies of water; they’re like lifelines, providing drinking water for millions of people and supporting wildlife.

Over the years, Lake Superior has come face-to-face with some serious challenges, like sediment runoff, microplastics, and harmful chemicals. How polluted is Lake Superior? Read on to learn more about what’s being done to save this pristine lake.

Is Lake Superior Safe to Swim In?

Duluth, Minnesota USA March 2, 2013 Surfer on Lake Superior near Duluth, Minnesota in the winter in the month of March.

You can swim or even surf in Lake Superior; prepare for cold water and strong currents.

Lake Superior is a gorgeous lake with a lot of swimming opportunities. Just beware; the waters are pretty cold, and there are dangerous currents to watch out for. As for pollution, Lake Superior is the cleanest of the five Great Lakes. The lake’s massive size helps dilute any pollutants that enter the water. Plus, it has fewer farms along its shores, reducing pollution. However, even though the lake is doing great, it could be doing better. Concerns are rising about pollution, with some of the pollution levels directly resulting from climate change.

Climate Change and Lake Superior

Heatwave hot sun. Climate Change. Global Warming. Thermometer high temperatures.

Climate change causes increased storm activity, which impacts lake water quality.

Lake Superior is beginning to show signs of vulnerability to the impacts of climate change. There’s been increased storm activity and rising water temperatures, which are causing problems with algal blooms. Blue-green algal blooms are often associated with warmer and nutrient-rich waters like Lake Erie. So it was a big shock to everyone when they began popping up all over Lake Superior, the coldest of all the Great Lakes. However, even though Lake Superior is the coldest, over the years, it’s been warming up at an alarming rate.


Climate change, increased precipitation, and nutrient runoff are believed to be contributing to the excessive algal blooms. The western region of Lake Superior has experienced major increases in precipitation. The rain washes nutrients into the lake, providing favorable conditions for blue-green algae. Some post-storm sediment plumes have been so large they’re visible from space.

Animal Feeding Operations

Basket Ball Indiana Style

Agricultural runoff contributes to the pollution in Lake Superior.

Concerns surrounding the potential for runoff pollution from concentrated animal feeding operations have been raised. Agricultural runoff has significantly contributed to the lake’s degraded water quality, increasing sediment, nutrient (phosphorus and nitrogen) levels, and potential contamination from E. coli bacteria.


Plastic, particularly microplastics, is now the largest contributor to marine pollution worldwide. While research on microplastic pollution has mainly focused on marine ecosystems, it is also prevalent in freshwater systems. One study shows the concentration of microplastics was higher in the north, west, and nearshore regions, possibly influenced by currents, water circulation patterns, and proximity to population centers.


Photograph of a mountain top that has been destroyed by logging. Brownish red dirt is visible where all of the trees have been clear-cut. Many tree trunks are seen in the center frame. The destroyed mountaintop is dimmed with live, green trees. In the background are mountain tops that have not been destroyed.

Deforestation is one of the biggest problems Lake Superior faces since it causes excess erosion.

Over time, Lake Superior has experienced varying levels of pollution and misuse. One of the biggest problems has been deforestation, the widespread clearing of forests. Deforestation has profound consequences on the environment, particularly in relation to water pollution. When forests are cut down, the protective cover of trees and their strong roots that anchor soil are lost. This makes the land vulnerable to erosion.

Moreover, forests absorb nutrients and sediment through the organic material on the forest floor. But, when forests are disturbed (or cut down), this delicate balance is disrupted. When the trees disappear, soil and sediment levels in nearby water bodies increase, threatening water quality.

Clearer Lakes Raise Concerns: Huron and Michigan

Large waves crashing along the Lake Michigan Shoreline at Simons Island Park in Kenosha Wisconsin on a beautiful sunny afternoon.

Lake Michigan has become clearer because of invasive mussel species eating plankton.

As for the other lakes around Superior, there’s been some interesting news about Lake Huron and Michigan. A study published in the Journal of Great Lakes Research found that lakes Huron and Michigan have become clearer in the past 20 years. You’d think a suddenly clearer lake would be a good thing, but it turns out the water clarity is mainly due to invasive species. Zebra and quagga mussels, an invasive species, improve the water quality by filtering out plankton. And the sudden light may be disrupting the food chain and impacting the growth of algae.

What Is Bioaccumulation?

Pollutants entering Lake Superior stay in the lake for a long time. These harmful substances also accumulate in the bodies of organisms as they move up the food chain. This is called bioaccumulation. While the initial chemical levels in the water may be low, they become highly concentrated in larger fish and other animals that eat smaller creatures.

The toxins can be dangerous for animals and humans who consume contaminated fish. Warnings against fish consumption have been issued in many states and in Ontario due to the high concentrations of toxins, such as PCBs (polychlorinated biphenyls). PCBs are basically a bunch of human-made chemicals that have carbon, hydrogen, and chlorine in them. These chemicals tend to gather in the muddy parts of lakes and can build up in the fatty tissues of fish, posing serious health risks.

PCBs are just the start. There are also forever chemicals to look out for. Also referred to as PFAS, these chemicals have a very slow degradation process. A recent study has discovered alarmingly high levels of PFAS, or forever chemicals, in fish found in the Great Lakes. The study examined over 500 fish samples from rivers, streams, and the Great Lakes. The highest levels of PFAS were found in fish from the Great Lakes. The chemicals called PFAS stick around in the Great Lakes for a long time because the water doesn’t flow as quickly as it does in the ocean.

Saving Lake Superior: Positive Developments

A girl swims in Lake Superior in the upper peninsula of Lake Michigan. Rocks are visable through the glass like, pristine waters. Pictured Rocks National Lakeshore is in the distance.

A joint effort between Canada and the United States can help protect Lake Superior.

Lake Superior’s history has been marked by triumphant moments. In the 1970s, Lake Superior had to deal with the management of sea lamprey populations. Fortunately, the United States and Canada collaborated effectively, successfully mitigating the issue through joint efforts.

Future team efforts can help protect this lake from giving way to pollution. For instance, the Great Lakes Water Quality Agreement has been a crucial turning point in addressing poor water quality through stricter waste disposal regulations and better agricultural practices. And while challenges persist, there is hope. Concentrations of certain chemicals like PCBs and PAHs are decreasing, although it will take several decades to eliminate them completely.

Great Lakes Water Quality Agreement

The Great Lakes Water Quality Agreement (GLWQA) is a special commitment to save the Great Lakes. The agreement aims to protect the “chemical, physical, and biological integrity” of the Great Lakes. It reflects the shared responsibility of both countries in restoring and maintaining the integrity of the Great Lakes while encouraging public participation in addressing water quality issues in the region. The promise was made between Canada and the U.S. a while ago, with the agreement signed in 1972.

Environmental Law and Policy Center

The Environmental Law & Policy Center (ELPC) is the Midwest’s leading nonprofit environmental law organization. They play a crucial role in safeguarding Lake Superior. To prevent the growth of toxic algae, ELPC actively monitors and litigates against phosphorus pollution stemming from concentrated animal feeding operations in the Maumee River watershed. They also address climate change by actively highlighting scientific findings, assessing risks, and advocating for the cleanup of pollutants.

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About the Author

Crystal is a dedicated writer at A-Z Animals, focusing on topics related to mammals, insects, and travel. With over a decade of experience in the world of research and writing, she also fulfills the role of a skilled video and audio engineer. Residing in sunny Florida, alligators are Crystal's favorite animal.

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