RESEARCH STARTER

Lake Superior

Lake Superior is the largest freshwater lake in the world by surface area, spanning approximately 31,820 square miles (82,410 square kilometers) and holding the third-largest volume of freshwater globally. Located on the border between the United States and Canada, it features a maximum depth of 733 feet (223 meters) and is surrounded by diverse ecosystems that include some of the oldest geological formations on Earth. The lake plays a significant role in regional climate, moderating temperatures and causing unique weather patterns, such as lake effect snow, which can result in substantial snowfall along its shores.

Lake Superior is home to over 80 fish species, supporting a rich aquatic food web, though it faces challenges from invasive species and pollution, particularly from historical mining activities. While the lake has historically been less polluted than its Great Lakes counterparts, ongoing environmental concerns, including mercury contamination, continue to affect its ecosystem. Human interaction with Lake Superior has evolved over centuries, with the region traditionally rich in minerals and wildlife, driving industries like mining and fishing.

Tourism plays a vital role in the local economy, with activities centered on hunting, fishing, and exploring natural sites like Isle Royale National Park and the Apostle Islands. Efforts to restore and protect the lake are ongoing, with initiatives aimed at addressing pollution and invasive species management through cooperative programs between the United States and Canada.

Full Article

  • Category: Inland Aquatic Biomes.
  • Geographic Location: North America.
  • Summary: The largest freshwater lake on Earth by surface area and the third-largest by volume, this is an ecosystem altered by overfishing, invasive species, and industrial activities.

Lake Superior exceeds all other lakes in the world by surface area, has the third-greatest volume of water for a freshwater lake, and contains the deepest point in the Great Lakes. While its formation during the last glaciation was geologically recent, on its shores lie some of the most ancient rocks on Earth. It is an inland ecological system that has been known by many names. In Ojibwe (Anishinaabemowin), the lake is called gichi-gami, meaning “great sea,” a name popularized in English as “Gitche Gumee.” Over the years, Lake Superior has undergone troubling changes in water quality and aquatic species.

Geography, Hydrology, Climate

With a surface area of 31,820 square miles (82,410 square kilometers), Lake Superior is the largest freshwater lake in the world by surface area. Containing 2,900 cubic miles (12,100 cubic kilometers) of water, it is the third-largest lake by volume, and contains more water than all of the other Great Lakes combined. In surface size, it spreads 350 miles (563 kilometers) in length and 160 miles (257 kilometers) in width, and is bounded by 2,726 miles (4,387 kilometers) of shoreline in Minnesota, Wisconsin, and Michigan in the US, as well as the Canadian province of Ontario along most of its northern waters.

So large is this lake that the summer sun sets about thirty-five minutes later on its western shore than its eastern shore. Its maximum depth is 1,332 feet (406 meters), and the lake bottom at its deepest location lies about 733 feet (223 meters) below sea level. Its surface averages 600 feet (183 meters) above sea level.

Like the other Great Lakes, Lake Superior occupies a basin shaped by continental glaciers during the last Ice Age. As the Laurentide Ice Sheet retreated, meltwater accumulated in the deepened basin, forming the modern lake. As the westernmost lake in the chain, Superior accepts water from more than 200 rivers. Water leaves the lake via the St. Marys River to Lake Huron.

Rock on the northern shore of Lake Superior is some of the oldest found on Earth. In particular, the north shore granites formed from magma in the Precambrian Period (between 4.5 billion and 540 million years ago).

Due to its large size, Lake Superior affects regional weather in several ways. Its waters hold the heat of summer and the cold of winter longer than the surrounding land, moderating temperatures as seasons change. Overall, the climate around Lake Superior is more maritime than inland temperate, and resembles Nova Scotia more than Ontario or the surrounding states.

The most pronounced impact is lake-effect snow, when westerly winds pick up moisture as they blow over the lake; upon reaching the colder eastern shore, heavy snow falls. Lake-effect snow extends 20 to 30 miles inland, primarily on the Ontario shore southeast of the town of Marathon, and from the transboundary city of Sault Ste. Marie to the Wisconsin-Michigan border, that is, nearly the entire south shore. Average annual snowfall in Michigan’s Keweenaw Peninsula exceeds 200 inches in places.

In December 2024, Lake Superior reached an average temperature of 44.2 degrees F. This was higher than the lake’s traditional average temperature of 40.5 degrees F. This sudden increase was attributed to global climate change. The lake seldom freezes over completely in winter; complete ice cover is rare; however, Lake Superior reached roughly 90–100 percent ice coverage in mid-February 2014. Indicators derived from the National Oceanic and Atmospheric Administration (NOAA) ice chart records show a long-term decline in Great Lakes ice cover concentration and duration over the period 1973–2020, with substantial year-to-year variability. Observed metrics indicate several changes in the lake. Summer surface water temperature has increased by 4.5 degrees F (2.5 degrees C) in the year beginning 1979, whereas summer temperature on the surrounding land has increased 2.7 degrees F (1.5 degrees C) during the same period.

While the lake water seems to be building up heat faster than the land, it may also be evaporating faster. In the summer of 2007, monthly historic surface-level lows were set: August at 0.67 feet (0.20 meters) below the norm, and September at 0.58 feet (0.18 meters) below the norm, which is 601 feet (183 meters). The situation turned around beginning in 2014, when cooler temperatures, more ice cover, and higher precipitation caused an increase in lake levels. By 2019, Lake Superior had reached record high levels, topping out at over 603 feet (184 meters). However, this trend reversed in the early 2020s, with Lake Superior measuring only 601.5 feet in November 2024. This was more than six inches lower than the same time in 2023 and the lowest recorded water level for the lake in a decade.

Biota

Lake Superior is an oligotrophic lake, meaning that it has a low nutrient budget because the surrounding soils release few nutrients. Its deep, cold waters are less productive than those of the other Great Lakes; still, it is home to a variety of species of fish and other organisms. The food web is based on the primary producers, the phytoplankton, here mainly green algae, blue-green algae, diatoms, and flagellates. These are consumed by a variety of filter-feeding animals, including zooplankton, shrimp, snails, and clams, which in turn are consumed by fish.

Over 80 species of fish have been recorded in the lake. These include key native species such as muskellunge (Esox masquinongy), pumpkinseed (Lepomis gibbosus), bloater (Coregonus hoyi), northern pike (Esox lucius), lake sturgeon (Acipenser fulvescens), longnose sucker (Catostomus catostomus), brook trout (Salvelinus fontinalis), and burbot (Lota lota).

Introduced fish in Lake Superior include freshwater drum (Aplodinotus grunniens), rainbow trout (Oncorhynchus mykiss), Atlantic salmon (Salmo salar), and brown trout (Salmo trutta)—as well as some particularly damaging invasive species, such as sea lamprey (Petromyzon marinus), round goby (Neogobius melanostomus), white perch (Morone americana), ruffe (Gymnocephalus cernuus), and various Asian carp species, such as the common carp (Cyprinus carpio).

This rich fish community forms the basis of a historically important commercial fishery, based especially on lake whitefish (Coregonus clupeaformis), yellow perch (Perca flavescens), rainbow smelt (Osmerus mordax), and cisco or lake herring (Coregonus artedi). The first records, from 1879, of commercial lake whitefish indicate 2,356 pounds (1,069 kilograms) of production. Fish populations have declined due to overfishing and parasitism by the nonnative sea lamprey, which attaches its mouth to other fishes and scrapes away the flesh with a sharp tongue and teeth. Affected fish often die from fluid loss and infection after several attacks.

Threatened plants in the Lake Superior biome include pitcher’s thistle (Cirsium pitcheri), which grows in the sandy beach and dune habitat at various points along the shore; Fassett’s locoweed (Oxytropis campestris var. chartacea), found between seasonal water-level highs and lows; American hart’s-tongue fern (Asplenium scolopendrium var. americana), a fern that prefers to grow upon stone surfaces; dwarf lake iris (Iris lacustris), a denizen of gravel, moist sand, and tree-shaded areas; and Houghton’s goldenrod (Solidago hoghtonii), which prefers moist environs such as limestone crevices and the swales between dunes.

Human Interaction

Unlike the other Great Lakes, Lake Superior does not have large cities or a dense population along its shore. The world’s farthest-inland port, Duluth (population 87,680 in 2023), sits on the far western point of the lake. Thunder Bay, Ontario, is the largest city on Lake Superior, with a population of 108,843 in the 2021 Canadian census. Because of this, Lake Superior has historically been the least polluted of the Great Lakes, but human activity still poses problems for the lake.

The Lake Superior region is rich in minerals and wildlife, and many towns and cities grew from mining settlements or fur trading posts. Iron, copper, silver, gold, nickel, and uranium are all mined in the area and transported via the lake to global markets. Iron, in particular, has been a major enterprise here. Between 1875 and the 1950s, iron mining dominated the industry on much of the north shore of Lake Superior, and contended with grain shipments for the top commodity shipped on its waters. This led to the expansion of the fleet of lake freighters that ply the Great Lakes, the St. Lawrence River, and thus to the Atlantic Ocean. Although mining techniques and locations have changed, it still comprises a significant portion of the industry and shipping traffic in the Lake Superior region, and contributes to pollution. In particular, the mining industry has introduced mercury into the water. This mercury is taken in by plankton and then carried up the food chain to fish that are caught and eaten by humans, which can be a health risk. While the amount of mercury released into the lake was highest in the late 1800s and early 1900s and declined afterward, large amounts of mercury made their way into the lake’s sediment at that time.

The French, and later other Europeans, entered the fur trade here in the seventeenth century. The eventual depletion of widely abundant populations of fur-bearing animals caused many settlers to leave the shores of Lake Superior; some companies reestablished farther west. Lake Superior attracts significant tourism, often taking the form of hunting and fishing participants. Isle Royale, Michigan, for example, which itself contains several lakes, boasts moose and wolf populations that bespeak its relatively intact habitat. Isle Royale is a US National Park; Madeline Island and the Apostle Islands in Wisconsin; and Grand Island, a National Recreation Area in Michigan, are other favorite destinations of boaters.

To combat pollution, the US and Canada in 1991 formed the Binational Program to Restore and Protect the Lake Superior Basin, a body committed to administering Lake Superior as a demonstration area to prohibit any point source discharge of any toxic, persistent substance. Zero discharge procedures and compliance are monitored by three groups: the Lake Superior Task Force, made up of senior managers from government and environmental bodies; the Lake Superior Work Group, providing technical direction and policy guidance; and the Lake Superior Binational Forum, where representatives from the public and industry regularly air the issues and examine solutions.

The Binational Program has since taken up related issues that affect the biome, such as a comprehensive attack on the deleterious impacts of invasive plant and animal species in Lake Superior. The group has initiatives for monitoring and prevention, ballast-water testing, mitigation and restoration measures for shoreline habitats, and outreach to such entities as permitting agencies, fishing outfitters and marinas, nurseries, and garden centers.


Bibliography

Farina, Gabrielle, and Haley, Thiem. “Several Great Lakes Experience Record-Warm Water Temperatures Heading into Winter.” Climate – NOAA, 9 Dec. 2024, www.climate.gov/news-features/event-tracker/several-great-lakes-experience-record-warm-water-temperatures-heading. Accessed 4 Mar. 2026.

Howarth, Tom. “How Lake Superior Water Levels Changed in 2024.” Newsweek, 30 Dec. 2024, www.newsweek.com/how-lake-superior-water-levels-changed-2024-2006610. Accessed 4 Mar. 2026.

Kennedy, Caitlyn. “Great Lakes Ice Cover Most Extensive since Mid-’90s.” Climate – NOAA, 26 Feb. 2014, www.climate.gov/news-features/event-tracker/great-lakes-ice-cover-most-extensive-mid-90s. Accessed 4 Mar. 2026.

“Lake Superior Climatology.” Great Lakes Integrated Sciences and Assessments, 2022, glisa.umich.edu/sustained-assessment/superior-climatology/. Accessed 4 Mar. 2026.

“Lake Superior.” Encyclopaedia Britannica, 29 Jan. 2026, www.britannica.com/place/Lake-Superior-lake-North-America. Accessed 4 Mar. 2026.

“Lake Superior.” Michigan Department of Environment, Great Lakes, and Energy, www.michigan.gov/egle/about/organization/water-resources/great-lakes-coordination/lake-superior. Accessed 4 Mar. 2026.

“Lake Superior.” United States Environmental Protection Agency (EPA), 18 Feb. 2026, www.epa.gov/greatlakes/lake-superior. Accessed 4 Mar. 2026.

Ostlie, Wayne. Great Lakes Ecological Assessment—Threatened and Endangered Plants. The Nature Conservancy, 1990.

Risjord, Norman K. Shining Big-Sea Waters: The Story of Lake Superior. Minnesota Historical Society Press, 2008.

Thomas, Amy, et al. Lake Superior Aquatic Invasive Species Complete Prevention Plan. Lake Superior Binational Program, 2009.

Full Article

  • Category: Inland Aquatic Biomes.
  • Geographic Location: North America.
  • Summary: The largest freshwater lake on Earth by surface area and the third-largest by volume, this is an ecosystem altered by overfishing, invasive species, and industrial activities.

Lake Superior exceeds all other lakes in the world by surface area, has the third-greatest volume of water for a freshwater lake, and contains the deepest point in the Great Lakes. While its formation during the last glaciation was geologically recent, on its shores lie some of the most ancient rocks on Earth. It is an inland ecological system that has been known by many names. In Ojibwe (Anishinaabemowin), the lake is called gichi-gami, meaning “great sea,” a name popularized in English as “Gitche Gumee.” Over the years, Lake Superior has undergone troubling changes in water quality and aquatic species.

Geography, Hydrology, Climate

With a surface area of 31,820 square miles (82,410 square kilometers), Lake Superior is the largest freshwater lake in the world by surface area. Containing 2,900 cubic miles (12,100 cubic kilometers) of water, it is the third-largest lake by volume, and contains more water than all of the other Great Lakes combined. In surface size, it spreads 350 miles (563 kilometers) in length and 160 miles (257 kilometers) in width, and is bounded by 2,726 miles (4,387 kilometers) of shoreline in Minnesota, Wisconsin, and Michigan in the US, as well as the Canadian province of Ontario along most of its northern waters.

So large is this lake that the summer sun sets about thirty-five minutes later on its western shore than its eastern shore. Its maximum depth is 1,332 feet (406 meters), and the lake bottom at its deepest location lies about 733 feet (223 meters) below sea level. Its surface averages 600 feet (183 meters) above sea level.

Like the other Great Lakes, Lake Superior occupies a basin shaped by continental glaciers during the last Ice Age. As the Laurentide Ice Sheet retreated, meltwater accumulated in the deepened basin, forming the modern lake. As the westernmost lake in the chain, Superior accepts water from more than 200 rivers. Water leaves the lake via the St. Marys River to Lake Huron.

Rock on the northern shore of Lake Superior is some of the oldest found on Earth. In particular, the north shore granites formed from magma in the Precambrian Period (between 4.5 billion and 540 million years ago).

Due to its large size, Lake Superior affects regional weather in several ways. Its waters hold the heat of summer and the cold of winter longer than the surrounding land, moderating temperatures as seasons change. Overall, the climate around Lake Superior is more maritime than inland temperate, and resembles Nova Scotia more than Ontario or the surrounding states.

The most pronounced impact is lake-effect snow, when westerly winds pick up moisture as they blow over the lake; upon reaching the colder eastern shore, heavy snow falls. Lake-effect snow extends 20 to 30 miles inland, primarily on the Ontario shore southeast of the town of Marathon, and from the transboundary city of Sault Ste. Marie to the Wisconsin-Michigan border, that is, nearly the entire south shore. Average annual snowfall in Michigan’s Keweenaw Peninsula exceeds 200 inches in places.

In December 2024, Lake Superior reached an average temperature of 44.2 degrees F. This was higher than the lake’s traditional average temperature of 40.5 degrees F. This sudden increase was attributed to global climate change. The lake seldom freezes over completely in winter; complete ice cover is rare; however, Lake Superior reached roughly 90–100 percent ice coverage in mid-February 2014. Indicators derived from the National Oceanic and Atmospheric Administration (NOAA) ice chart records show a long-term decline in Great Lakes ice cover concentration and duration over the period 1973–2020, with substantial year-to-year variability. Observed metrics indicate several changes in the lake. Summer surface water temperature has increased by 4.5 degrees F (2.5 degrees C) in the year beginning 1979, whereas summer temperature on the surrounding land has increased 2.7 degrees F (1.5 degrees C) during the same period.

While the lake water seems to be building up heat faster than the land, it may also be evaporating faster. In the summer of 2007, monthly historic surface-level lows were set: August at 0.67 feet (0.20 meters) below the norm, and September at 0.58 feet (0.18 meters) below the norm, which is 601 feet (183 meters). The situation turned around beginning in 2014, when cooler temperatures, more ice cover, and higher precipitation caused an increase in lake levels. By 2019, Lake Superior had reached record high levels, topping out at over 603 feet (184 meters). However, this trend reversed in the early 2020s, with Lake Superior measuring only 601.5 feet in November 2024. This was more than six inches lower than the same time in 2023 and the lowest recorded water level for the lake in a decade.

Biota

Lake Superior is an oligotrophic lake, meaning that it has a low nutrient budget because the surrounding soils release few nutrients. Its deep, cold waters are less productive than those of the other Great Lakes; still, it is home to a variety of species of fish and other organisms. The food web is based on the primary producers, the phytoplankton, here mainly green algae, blue-green algae, diatoms, and flagellates. These are consumed by a variety of filter-feeding animals, including zooplankton, shrimp, snails, and clams, which in turn are consumed by fish.

Over 80 species of fish have been recorded in the lake. These include key native species such as muskellunge (Esox masquinongy), pumpkinseed (Lepomis gibbosus), bloater (Coregonus hoyi), northern pike (Esox lucius), lake sturgeon (Acipenser fulvescens), longnose sucker (Catostomus catostomus), brook trout (Salvelinus fontinalis), and burbot (Lota lota).

Introduced fish in Lake Superior include freshwater drum (Aplodinotus grunniens), rainbow trout (Oncorhynchus mykiss), Atlantic salmon (Salmo salar), and brown trout (Salmo trutta)—as well as some particularly damaging invasive species, such as sea lamprey (Petromyzon marinus), round goby (Neogobius melanostomus), white perch (Morone americana), ruffe (Gymnocephalus cernuus), and various Asian carp species, such as the common carp (Cyprinus carpio).

This rich fish community forms the basis of a historically important commercial fishery, based especially on lake whitefish (Coregonus clupeaformis), yellow perch (Perca flavescens), rainbow smelt (Osmerus mordax), and cisco or lake herring (Coregonus artedi). The first records, from 1879, of commercial lake whitefish indicate 2,356 pounds (1,069 kilograms) of production. Fish populations have declined due to overfishing and parasitism by the nonnative sea lamprey, which attaches its mouth to other fishes and scrapes away the flesh with a sharp tongue and teeth. Affected fish often die from fluid loss and infection after several attacks.

Threatened plants in the Lake Superior biome include pitcher’s thistle (Cirsium pitcheri), which grows in the sandy beach and dune habitat at various points along the shore; Fassett’s locoweed (Oxytropis campestris var. chartacea), found between seasonal water-level highs and lows; American hart’s-tongue fern (Asplenium scolopendrium var. americana), a fern that prefers to grow upon stone surfaces; dwarf lake iris (Iris lacustris), a denizen of gravel, moist sand, and tree-shaded areas; and Houghton’s goldenrod (Solidago hoghtonii), which prefers moist environs such as limestone crevices and the swales between dunes.

Human Interaction

Unlike the other Great Lakes, Lake Superior does not have large cities or a dense population along its shore. The world’s farthest-inland port, Duluth (population 87,680 in 2023), sits on the far western point of the lake. Thunder Bay, Ontario, is the largest city on Lake Superior, with a population of 108,843 in the 2021 Canadian census. Because of this, Lake Superior has historically been the least polluted of the Great Lakes, but human activity still poses problems for the lake.

The Lake Superior region is rich in minerals and wildlife, and many towns and cities grew from mining settlements or fur trading posts. Iron, copper, silver, gold, nickel, and uranium are all mined in the area and transported via the lake to global markets. Iron, in particular, has been a major enterprise here. Between 1875 and the 1950s, iron mining dominated the industry on much of the north shore of Lake Superior, and contended with grain shipments for the top commodity shipped on its waters. This led to the expansion of the fleet of lake freighters that ply the Great Lakes, the St. Lawrence River, and thus to the Atlantic Ocean. Although mining techniques and locations have changed, it still comprises a significant portion of the industry and shipping traffic in the Lake Superior region, and contributes to pollution. In particular, the mining industry has introduced mercury into the water. This mercury is taken in by plankton and then carried up the food chain to fish that are caught and eaten by humans, which can be a health risk. While the amount of mercury released into the lake was highest in the late 1800s and early 1900s and declined afterward, large amounts of mercury made their way into the lake’s sediment at that time.

The French, and later other Europeans, entered the fur trade here in the seventeenth century. The eventual depletion of widely abundant populations of fur-bearing animals caused many settlers to leave the shores of Lake Superior; some companies reestablished farther west. Lake Superior attracts significant tourism, often taking the form of hunting and fishing participants. Isle Royale, Michigan, for example, which itself contains several lakes, boasts moose and wolf populations that bespeak its relatively intact habitat. Isle Royale is a US National Park; Madeline Island and the Apostle Islands in Wisconsin; and Grand Island, a National Recreation Area in Michigan, are other favorite destinations of boaters.

To combat pollution, the US and Canada in 1991 formed the Binational Program to Restore and Protect the Lake Superior Basin, a body committed to administering Lake Superior as a demonstration area to prohibit any point source discharge of any toxic, persistent substance. Zero discharge procedures and compliance are monitored by three groups: the Lake Superior Task Force, made up of senior managers from government and environmental bodies; the Lake Superior Work Group, providing technical direction and policy guidance; and the Lake Superior Binational Forum, where representatives from the public and industry regularly air the issues and examine solutions.

The Binational Program has since taken up related issues that affect the biome, such as a comprehensive attack on the deleterious impacts of invasive plant and animal species in Lake Superior. The group has initiatives for monitoring and prevention, ballast-water testing, mitigation and restoration measures for shoreline habitats, and outreach to such entities as permitting agencies, fishing outfitters and marinas, nurseries, and garden centers.


Bibliography

Farina, Gabrielle, and Haley, Thiem. “Several Great Lakes Experience Record-Warm Water Temperatures Heading into Winter.” Climate – NOAA, 9 Dec. 2024, www.climate.gov/news-features/event-tracker/several-great-lakes-experience-record-warm-water-temperatures-heading. Accessed 4 Mar. 2026.

Howarth, Tom. “How Lake Superior Water Levels Changed in 2024.” Newsweek, 30 Dec. 2024, www.newsweek.com/how-lake-superior-water-levels-changed-2024-2006610. Accessed 4 Mar. 2026.

Kennedy, Caitlyn. “Great Lakes Ice Cover Most Extensive since Mid-’90s.” Climate – NOAA, 26 Feb. 2014, www.climate.gov/news-features/event-tracker/great-lakes-ice-cover-most-extensive-mid-90s. Accessed 4 Mar. 2026.

“Lake Superior Climatology.” Great Lakes Integrated Sciences and Assessments, 2022, glisa.umich.edu/sustained-assessment/superior-climatology/. Accessed 4 Mar. 2026.

“Lake Superior.” Encyclopaedia Britannica, 29 Jan. 2026, www.britannica.com/place/Lake-Superior-lake-North-America. Accessed 4 Mar. 2026.

“Lake Superior.” Michigan Department of Environment, Great Lakes, and Energy, www.michigan.gov/egle/about/organization/water-resources/great-lakes-coordination/lake-superior. Accessed 4 Mar. 2026.

“Lake Superior.” United States Environmental Protection Agency (EPA), 18 Feb. 2026, www.epa.gov/greatlakes/lake-superior. Accessed 4 Mar. 2026.

Ostlie, Wayne. Great Lakes Ecological Assessment—Threatened and Endangered Plants. The Nature Conservancy, 1990.

Risjord, Norman K. Shining Big-Sea Waters: The Story of Lake Superior. Minnesota Historical Society Press, 2008.

Thomas, Amy, et al. Lake Superior Aquatic Invasive Species Complete Prevention Plan. Lake Superior Binational Program, 2009.

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