The Great Lakes are a chain of five large, freshwater lakes that are located in central North America, astride the border of Canada and the United States. The Great Lakes include Lake Erie, Lake Huron, Lake Michigan, Lake Ontario, and Lake Superior and together form the largest group of freshwater lakes on Earth. They are contained within the Great Lakes watershed, a region whose waters discharge into the Saint Lawrence River and, ultimately, the Atlantic Ocean.
The Great Lakes cover a total surface area of 95,000 square miles and hold about 5,500 cubic miles of water (approximately 20 percent of all the world's fresh water and more than 80 percent of the fresh water of North America). There are more than 10,000 miles of shoreline that frame the Great Lakes and from west to east, the lakes span more than 750 miles.
The Great Lakes formed during the Pleistocene Epoch as the result of the repeated glaciation of the region during the Ice Ages. Glaciers advanced and retreated time and again, gradually carving deep depressions in the Great Lakes River Basin. When the glaciers receded at the end of the last glacial period about 15,000 years ago, the Great Lakes filled with water left behind by the melting ice.
The Great Lakes and their surrounding lands encompass a wide variety of freshwater and terrestrial habitats including coniferous and hardwood forests, freshwater marshes, freshwater wetlands, dunes, grasslands, and prairies. The Great Lakes region supports a diverse fauna that includes numerous species of mammals, amphibians, birds, reptiles, and fishes.
There are more than 250 species of fishes found in the Great Lakes including Atlantic salmon, bluegill, brook trout, Chinnok salmon, Coho salmon, freshwater drum, lake sturgeon, lake trout, lake whitefish, northern pike, rock bass, walleye, white perch, yellow perch, and many others. Native mammals include the black bear, fox, elk, white-tailed deer, moose, beaver, river otter, coyote, gray wolf, Canada lynx, and many others. Bird species native to the Great Lakes include herring gulls, whooping cranes, snowy owls, wood ducks, great blue herons, bald eagles, piping plovers, and many more.
The Great Lakes have suffered greatly the effects of introduced (non-native) species during the past two hundred years. Non-native animal species such as zebra mussels, quagga mussels, sea lampreys, alewive, Asian carps, and many others have greatly altered the Great Lakes ecosystem. The most recent non-native animal to have been recorded in the Great Lakes is the spiny water flea, a crustacean native to the seas of the Middle East that is now quickly populating Lake Ontario.
Introduced species compete with native species for food and habitat and can also More than 180 non-native species have entered the Great Lakes since the latter part of the 19th century. Many of the introduce species have been transported into the Great Lakes in the ballast water of ships, but other species such as the Asian carp, have invaded the lakes by swimming through the man-made channels and locks that now connect the Lake Michigan to the Mississippi River.
The following are the key characteristics of the Great Lakes:
- largest group of freshwater lakes on Earth
- account for 20 percent of all the world's fresh water
- account for more than 80 percent of the fresh water of North America
- introduced species have greatly altered the Great Lakes ecosystem
- supports more than 3,500 species of plants and animals
Animals of the Great Lakes
Some of the animals that inhabit the Great Lakes include:
- Lake whitefish (Coregonus clupeaformis) - The lake whitefish is a species of freshwater fish that belongs to the salmon family. Lake whitefish are found in all of the Great Lakes and are a valuable commercial species. Lake whitefish feed on bottom-dwelling invertebrates such as snails, clams, and the aquatic larvae of insects.
- Walleye (Sander vitreus) - The walleye is large freshwater fish native to the Great Lakes as well as most parts of Canada and the northern United States. Walleye are much recognized as icons of the places they inhabit—they are the state fish of Minnesota and South Dakota and they are the official fish of Saskatchewan.
- Yellow perch (Perca flavescens) - The yellow perch is a species of perch whose range includes the Great Lakes and the Saint Lawrence River. Adult yellow perch feed on aquatic insect larvae, crustaceans, mysid shrimp, fish eggs, and small fish.
- Great blue heron (Ardea herodias) - The great blue heron is a large wading bird common to freshwater wetland habitats throughout North American, including the Great Lakes. Great blue herons have a long, sharp bill that they use to capturea variety of small prey animals such as fish, crustaceans, insects, rodents, amphibians, reptiles, and birds.
- Canada lynx (Lynx canadensis) - The Canada lynx is a medium-sized cat that inhabits the forests throughout Canada and Alaska. In the Great Lakes region, Canada lynx occur around Lake Superior and on the northern shores of Lake Ontario and Georgian Bay, a large bay of Lake Huron that lies in Ontario, Canada. Canada lynxes are secretive, nocturnal mammals that feed on snowshoe hares, rodents and birds.
- Moose (Alces alces) - The moose is the largest living member of the deer family. Moose inhabit the forests that border the northern shores of the Great Lakes. Moose are herbivores that feed on a variety of herbaceous plants and grasses.
- Common snapping turtle (Chelydra serpentina) - The common snapping turtle is a widespread turtle that inhabits freshwater wetlands east of the Rocky Mountains, including the Great Lakes region. Snapping turtles have a reputation for being quite aggressive.
- American bullfrog (Lithobates catesbeiana) - The American bullfrog is a large frog that occurs in wetlands in the Great Lakes region. American bullfrogs are predators that feed on small mammals, reptiles, and invertebrates.
Great Lakes Environmental Research Laboratory. About Our Great Lakes. Accessed November 22, 2013. Published online at http://www.glerl.noaa.gov/pr/ourlakes/intro.html
Harding JH. Amphibians and Reptiles of the Great Lakes Region. University of Michigan Press; 1997. 400 p.
Kurta, A. Mammals of the Great Lakes Region. Revised Edition. University of Michigan Press; 1995. 392 p.
US Environmental Protection Agency. The Great Lakes: An Environmental Atlas and Resource Book. 2012. Published online at http://www.epa.gov/glnpo/atlas/index.html
US Environmental Protection Agency. Great Lakes Invasive Species. Accessed November 22, 2013. Published online at http://www.epa.gov/glnpo/invasive/