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Superior Facts | 3-quadrillion Gallons, One Great Lake

Physical Facts

  • Surface Area: 31,700 mi2 (82,100 km2):
    The size of the state of Maine
  • Volume: Roughly 3-quadrillion gallons
    (2900 mi3 (12,100 km3)):
    Enough to cover North and South America in one foot of water
  • Average Depth: 483 ft (147 m):
    About the distance between Lake Superior and Duluth's hilltop
  • Maximum Depth: 1,332 ft (406 m):
    The same as one lap around a standard track
  • Length: 350 mi (560 km):
    A drive from Two Harbors to Madison
  • Breadth: 160 mi (260 km):
    A drive from Duluth to Minneapolis
  • Shoreline Length: 1,826 mi (2,938 km):
    A drive from Duluth to Miami
  • Retention Time: 191 years:
    The average drop of water entered when Fort Snelling was a frontier outpost and Minneapolis didn't exist
  • Alternative Names: gichigami (Ojibwa), Lac Superieur (French), Gitche Gumee
    (from The Song of Hiawatha and The Wreck of the Edmunds Fitzgerald)

Lake Superior ...

  • is the largest freshwater lake in the world by surface area and the third largest by volume (Lake Baikal in Siberia and Lake Tanganyika in East Africa contain more water).
  • could hold all the water in the other Great Lakes, plus THREE MORE Lake Eries.
  • connects the heart of North America to a global economy.
  • is remarkably clean and cold.
  • is a geological newcomer (only about 10,000 years old).
  • is exhibiting a trend in summer surface temperature. Per decade since 1980, surface water temperature in summer has increased about 2 °F (1 °C), while regional air temperature has increased 1 °F (0.5 °C).
  • is managed through a binational agreement involving Canada and the U.S., and by the Province of Ontario and the states of Minnesota, Wisconsin, and Michigan.
  • has rip currents that are dangerous to swimmers.
  • holds 10% of the world's fresh surface water that is not frozen in a glacier or ice cap.

Created by Fire and Ice

  • 1 billion years ago: Molten basalt erupts from the Mid-Continent Rift. The rifting lasts for about 20 million years.
  • 950 million years ago: The rifting produces a blanket of basalt up to 10 mi (16 km) thick that slowly sinks into the earth creating the Lake Superior basin. Ancient rivers deposit the rocks that make up the Apostle Islands, Bayfield Peninsula, and Pictured Rocks National Park.
  • 500 million years ago: The area stabilizes.
  • 2.5 million years ago: Ice Age! Ice sculpts the basin into its present shape through glacial and interglacial periods.
  • 11,000 years ago: Glacial Lake Duluth, the precursor to Lake Superior, forms as the ice sheet retreats northeastward. The lake's torrential outflow near present-day Duluth carves the St. Croix River Valley and feeds the Mississippi River.
  • 10,000 years ago: During the retreat of glacial ice, western Lake Superior fluctuates, rising 500 ft (152 m) above or falling 250 ft (76 m) below its current level. Eventually, the St. Marys River becomes Superior's outflow, and the water level eases to its present state. Paleo-Indian people move into the Lake Superior region.
  • Today: The basin continues to spring back after being squashed by the last glacier. This "isostatic rebound" is greatest along Canadian shores, which are rising about 18 in (46 cm) per century. Lake levels continue to fluctuate.


  • Water level: depends on precipitation and the season. Typically, the lake is just over a foot (32 cm) higher in September than it is in March (NOAA's Great Lakes Water Level Observations). The annual average is 601.8 ft (183.4 m) above sea level.
  • Water budget: reflects about a 4-foot (125-cm) exchange of incoming and outgoing water each year. Superior has a relatively small watershed (49,300 mi2, 127,700 km2) for its size. This watershed is laced with streams that feed Lake Superior's 848 tributaries. Water has basically two ways out of Lake Superior: a right exit or up. Lake Superior spills toward the Atlantic Ocean through the Soo Locks on the St. Marys River. This eastern exit is about 600 ft (180m) above sea level. Contrary to what one might guess, Lake Superior evaporates fastest from October to February when dry cold air from Canada moves over the warmer surface of Lake Superior soaking up water like a sponge.
  • Seiches mask Superior's tiny tide. Seiches slosh through Lake Superior's basin after wind or high barometric pressure pushes water to one side and then quits pushing. In Lake Superior, seiches take roughly 8 hours to cross the basin and come back again, sometimes changing nearshore water levels by more than 3 ft (91 cm).
  • Water Temperature: exceptionally cold (average 40 °F (4 °C)) but swimmable in summer when the surface water warms.
  • Productivity: low. Since glaciers carved away much of the soil, Lake Superior is relatively unproductive (oligotrophic). With little in the way of plant nutrients and large amounts of dissolved oxygen, some scientists have called Lake Superior "a distilled water ice bath."
  • Underwater Visibility: superb, sometimes exceeding 75 ft (23 m).
  • Chemical Pollutants: Most (such as mercury, dioxin, and PCBs) fall from the atmosphere with precipitation or dust. Even though the concentrations of these toxins are relatively low compared to the other Great Lakes, they can accumulate through the aquatic food web and harm top predators, like bald eagles and humans.


Climate is the set of meteorological conditions that prevail in a region over time. Lake Superior's climate reflects its position on the planet and, to a smaller degree, the heat storage capacity of all the water it contains. It's in the cool part of North America's temperate zone where summers average about 70 °F (21 °C) and winters involve snow, parkas, and temperatures well below 0 °F (-18 °C). Of the roughly 30 inches (76 cm) of precipitation that hits the lake each year, most falls between May and October. Collisions between belts of low and high pressure from the Gulf of Mexico and Canada generate the region's wildest storms and blizzards. Scientists report that Lake Superior is responding to a global climate trend as clearly as anywhere on Earth. They've documented:

  • A decline in ice cover (Down by 79% since the 1970s).
  • An increase in surface water temperatures (Summer water surface temperatures have risen about 2 °F (1 °C) per decade since the 1980s).
  • Faster winds (Wind speeds have increased over the lake by nearly 5% per decade since the 1980s).
  • The regional trend is toward warmer temperatures, and increases in extreme storms and droughts. Winter and spring are showing signs of becoming wetter while summer and fall are showing signs of becoming drier.

Read more about Lake Superior's climate


Lake effect snow heading south-east. Photo by NASA's Earth Observatory

Weather is the state of the atmosphere with respect to current temperature, precipitation, wind, and cloudiness. Lake Superior can modify the daily weather through a phenomenon known as "lake effect." Compared to inland temperatures, shoreline temperatures can be noticeably warmer in winter and much cooler in summer. This is because water is slower to absorb and release heat than land. The "lake effect" can also super-size storms by adding moisture and speed to wind passing over the lake. Michigan's Upper Peninsula is typically buried under six times more snow each year than downtown Duluth because of the lake effect. In summer, a dome of high pressure can form over the lake pushing approaching storms to the southeast. The dangerous "Gales of November" occur in autumn when low-pressure systems pass over the lake. Wind speeds can easily reach 50 mph and gusts can exceed 100 mph. Fog hides Duluth under a heavy blanket for 52 days in an average year (by comparison, Minneapolis averages 11 days). Fog forms when temperature and dewpoint differ by less than 4 °F (2.5 °C). As the moisture in warm air condenses over the colder surface waters, advection fog rolls into Lake Superior's coastal communities. Sea smoke occurs when seriously cold air moves over relatively warmer water during winter.


Principle Cargos by Tonnage

From mid-March to mid-January the Soo Locks are open and Lake Superior supports an active maritime industry. The "Great Lakes Bulk Cargo Capital" of Duluth/Superior is one of the busiest inland ports in the United States. Each year the port handles about 1,000 ships carrying 42-million tons (38 metric tons) worth $1.9 billion. The largest of these ships, the lakers, are typically 1,000 ft (300 m) long and 105 ft (32 m) wide. They can't fit through the Welland Canal, so they will never ply the oceans. Mainly they carry coal and iron ore. Salties are ocean-going vessels. About 100 times per year a saltie makes the seven-day, 16-lock, 2,342-mile trip from the Atlantic Ocean through the Great Lakes-St. Lawrence Seaway to the Duluth/Superior Harbor to pick up grain, to drop off wind-energy equipment, or to conduct other business.


Tourism is one of the economic mainstays of the Lake Superior region, which is home to over 600,000 people (474,150 Americans and 155,675 Canadians). An abundance of festivals, concerts, events, and unique dining and shop-ping opportunities create a cheerful atmosphere, particularly in Lake Superior's two metro areas: Duluth, Minnesota, and Thunder Bay, Ontario. Summer brings boaters, sightseers, campers, kayakers, anglers, and even swimming sunbathers to the shore. Beachgoers should know how to escape from the rip currents that can form along Lake Superior's south shore. Known for its clean water, Lake Superior's water is a Mid-west SCUBA diving epicenter for sunken ships. In June, runners from around the world vie to win "Grandma's Marathon." Winter excites skiers, snowmobilers, snowshoers, and ice fishing fans. The Bayfield sea caves near the Apostle Islands in Wisconsin are worth a trek during years with enough ice cover. Every January, thousands gather along Minnesota's North Shore to cheer on the dogs and the mushers during the John Beargrease Sled Dog Marathon, a 400-mile journey that re-traces part of the region's history. All recreationists, but especially those who venture out in winter, should dress and behave to avoid hypothermia.

Lake Superior Fish

Native Species

Native fish

Lake Superior has bragging rights when it comes to fish. Although it produces far fewer fish than the other Great Lakes, it supports a robust suite of native species. Sustainable management practices have fostered a modern and commercially important fisheries industry after overfishing and the introduction of invasive species jeopardized it during the mid-1900s. Commercially caught fish include ciscoes (lake herring), chubs (deepwater ciscoes), lake whitefish, lake trout, and the non-native rainbow smelt. Lake Superior also supports a strong charter fishing industry and sportfishing opportunities focused on several species of salmon and trout.

Ciscoes were called lake herring by Scandinavian settlers, who thought they resembled ocean herring. Particularly during the spawning run in November, commercial fishermen harvest ciscoes for fillets, gefilte fish, and caviar destined for national and international markets. Ciscoes are a fantastic source of omega-3 fatty acids and are a regional smokehouse and restaurant favorite.

Lake whitefish live in deep waters mainly along Lake Superior's South Shore. Lake whitefish are prized for their delicate fillets and, like ciscoes, are lower on the food chain than lake trout and consequentially contain fewer bioaccumulative toxins.

Lake trout have made an astonishing recovery since their near-extinction in the late 1960s. If it weren't for the sea lamprey control program run by Canada and the U.S., Lake Superior's lean lake trout would not be on regional menus or available for sport fishing. The most abundant form of lake trout is the deep-dwelling siscowet.

When commercial fishing was in its heyday, lake sturgeon were hard-hit. Today, commercial harvest is prohibited and First Nations are only allowed to use them for ceremonial purposes. Lake sturgeon primarily swim in larger Canadian tributaries but restoration efforts in the St. Louis estuary seem to be paying off with the sighting of fry in 2011.

Non-native Species

Non-Native species

Non-native species have influenced the greatest of the Great Lakes since the early 1900s when rainbow trout and brown trout were intentionally introduced. From parasites to plants to fish, 97 non-native species are living in Lake Superior. An additional 24 non-native plants grow along Lake Superior's shores.

Currently, the worst Lake Superior offender is the sea lamprey. In vampirish fashion, they attach to large fish and suck their blood and body fluids out. They can consume roughly 40 lbs (18 kg) of fish in 12 to 18 months. Sea lamprey arrived in the upper Great Lakes once the Welland Canal allowed them to swim around Niagara Falls. The U.S. and Canada spend about $16 million annually to keep them in check in the Great Lakes.

Zebra mussels and their cousins, quagga mussels, don't plague Lake Superior like they do the other Great Lakes. However, they occupy the Duluth Superior Harbor along with dozens of species that were likely brought into the Great Lakes through ballast water.

During the 1970s, introduced rainbow smelt were the most abundant fish in Lake Superior. Fisheries experts aren't sure exactly why, but the smelt population crashed in 1979 and has stayed low ever since. Undaunted, smelters still brave cold Superior nights to net them as an annual rite of spring. Non-native species can damage the environment as well as local economies. Do your part to prevent the spread of non-native species. Don't release animals and plants into a body of water unless they came out of that body of water. Be sure to clean your boat and gear before leaving a lake, river or stream.

Terms to Know

  • Seiche: (pronounced "saysh") Also called a slosh. These "free standing-wave oscillations" rocking back and forth across lakes are created by wind or air pressure. You can set up a similar motion in your bathtub by sliding back and forth.
  • Oligotrophic: Very unproductive; lakes low in nutrients and algae, usually very transparent with abundant oxygen.
  • Soo Locks: A set of 5 locks on the St. Marys River separating Lake Superior and Lake Huron.
  • Lakers: They're not a basketball team! They're ships designed especially for transport on the Great Lakes.
  • Salties: Ocean-going vessels from all over the world.
  • Lake Effect: The ability of a large lake to modify the local weather.
  • Lake Superior Agate: Minnesota's official state gemstone. Quartz stones banded with rich reds and oranges (derived from iron ore in the soil) formed in the gas pockets of lava flows. Glaciers dispersed them in the last Ice Age.
  • Taconite: Sedimentary rock mined for its iron content of 25-30%. It is an important source of raw material for making steel.

Text adapted from:

Habermann, R., S. Moen, and E. Stykel. 2012. Superior Facts. Minnesota Sea Grant (pub. S25), Duluth, Minn.


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Blanken, Peter D., Christopher Spence, Newell Hedstrom, and John D. Lenters. 2011. "Evaporation from Lake Superior: 1. Physical controls and processes." Journal of Great Lakes Research, 707-716.

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Henson, Bonnie L., Daniel T. Kraus, Michael J. McMurtry, and David N. Ewert. 2010. Islands of Life: A Biodiversity and Conservation Atlas of the Great Lakes Islands, 20. Nature Conservancy of Canada. 154pp.

Hinkel, K. M., and F.E. Nelson. 2012. "Spatial and temporal aspects of the lake effect on the southern shore of Lake Superior." (accessed January 31, 2012).

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"Lake Superior." 2009. Wisconsin Department of Natural Resources. (accessed 21, 2012). Lemay, Konnie. 2012. "State of the Lake." Lake Superior Magazine, 19-27.

Lenters, J.D. 2004. "Trends in the Lake Superior water budget since 1948: a weakening seasonal cycle." Journal of Great Lakes Research (Supplement 1), 20-40.

Neff, Brian P. and J.R. Nicholas. 2005. "Uncertainty in the Great Lakes Water Balance: U.S. Geological Survey Scientific Investigations Report 2004-5100, 42. (accessed February 21, 2012.)

Quinn, F. H. and R. N. Kelley. 1983. Great Lakes Monthly Hydrologic Data. NOAA Data Report ERL GLERL-26, National Technical Information Service. (accessed February 17, 2012).

"Superior Trout Streams: How many are there?" 2012. Lake Superior Streams. http://www.lakesuperiorstreams.org/northshore/howmanytroutstreams.html (accessed March 6, 2012).

Wang, Jia, Bai Xuezhi, Haohuo Hu, Anne Clites, Marie Colton, and Brent Lofgren. 2011. "Temporal and Spatial Variability of Great Lakes Ice Cover, 1973-2010." Journal of Climate, 1-12.

Wilcox, D.A, T.A. Thompson, R.K. Booth, and J.R. Nicholas. 2007. Lake-level variability and water availability in the Great Lakes: U.S. Geological Survey Circular 1311.

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