Environment

What Are The Primary Inflows And Outflows Of Lake Superior?

The St. Marys River is the primary outflow that drains Lake Superior.

Lake Superior is the largest of North America's Great Lakes and borders the Canadian province of Ontario and the three US states of Minnesota, Wisconsin, and Michigan. It is the largest freshwater lake in the world by surface area, and with a volume of 2,900 cubic miles, Lake Superior also ranks as the world’s third-largest freshwater lake by volume. The lake measures 483 feet deep, 160 miles wide, and 350 miles long. The retention time of Lake Superior is 191 years, meaning that a drop of water that enters the lake will remain in the lake for an average of 191 years before emptying through the St. Marys River. The large lake includes numerous islands, such as Isle Royale, Slate Islands, Michipicoten Island, and the Apostle Islands.

Primary Inflows of Lake Superior

Lake Superior has numerous primary inflows, including the Nipigon, St. Louis, Pigeon, Pic, and Michipicoten rivers. These rivers are the larger of the more than 200 rivers that feed the lake.

Nipigon River

The Nipigon River is about 30 miles long and its width ranges between 160 and 660 feet. wide. Located in the Thunder Bay District of northwestern Ontario, Canada, the Nipigon is a fast-moving river that is home to the world's largest brook trout.  

St. Louis River

The St. Louis River has a length of 194 miles and serves as the primary reservation fishery of Lake Superior. The river flows through Minnesota and Wisconsin, temporarily becomes a freshwater estuary, and eventually drains into Lake Superior.

Pigeon River

The Pigeon River forms part of the US-Canada border, between the province of Ontario and the state of Minnesota. It is 31.2 miles in length and flows eastwards from the Boundary Waters Canoe Area Wilderness into Lake Superior.

Pic River

The Pic River is located in the eastern part of the Ontario's Thunder Bay District. The river is 93 miles in length and flows from Lake McKay, passes through the community of Longlac, and empties into Lake Superior near the town of Marathon.

Michipicoten River

The Michipicoten River is 70 miles in length and is located in the Algoma District of Ontario, Canada. The river originates in Dog Lake, joins the Magpie River, and finally drains into Michipicoten Bay on Lake Superior. As it flows west to Lake Superior, the Michipicoten River flows through two major lakes, namely Whitefish and Manitowik.

Primary Outflows of Lake Superior

The St. Marys River empties Lake Superior and drains into Lakes Huron, which is also a North American Great Lake. The full course of the river forms part of the international border separating Ontario, Canada from Michigan, USA. The St. Marys River has numerous tributaries. In the US, these tributaries include the Gogomain, Munuscong, and Charlotte rivers, while its Canadian tributaries include the Garden, Bar, and Root rivers. The river runs between the Upper Peninsula of Michigan and Ontario, flows through a network of canals, a dam containing 16 control gates, and hydropower plants. The International Lake Superior Board of Control determines the intervals at which water is released into the rapids, and such decisions are based on Lake Superior’s water levels. The board also balances the environmental and socio-economic interests of Lake Superior, as well as those of Lakes Michigan and Huron.

Lake Superior’s Ecosystem

Lake Superior is an oligotrophic environment, meaning that it has low productivity of organic compounds and nutrient content. Consequently, the lake produces little algae and therefore contains clear water with high underwater visibility of 27 feet. It hosts over 80 species of fish, such as the yellow perch, lake trout, longnose sucker, and lake whitefish. Lake Superior is also home to numerous mammals, birds, and plants.

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