North America’s Great Lakes—a chain of five interconnected inland lakes that form a major part of the border between the United States and Canada—hold a little more than 20% of the world’s entire freshwater supply. In addition to this impressive size, Lakes Superior, Huron, Michigan, Erie, and Ontario are “great” as economic engines, giving inland cities like Toronto and Chicago access to the Atlantic Ocean. The five Great Lakes and their exit waterway, the St. Lawrence River, border eight U.S. states and two Canadian provinces, and some 85 million people utilize them for water, natural resources, commerce, and recreation. 

　　Map showing the five Great Lakes of America.

Formation, Climate, and Ecology

The Great Lakes are relatively young glacial lakes—they began forming some 14,000 years ago as glaciers receded northward, leaving indentations and gashes in the landscape that slowly filled with water from feeder rivers. The lakes may have reached their current form only 3,000 years ago. Today the Great Lakes exist in a humid continental climate zone, with cold winters and warm summers being moderated a bit by the more stable temperature of the lake water. Minus the impacts of human development, the surrounding area is heavily forested and supportive of a wide range of birds and wildlife. As pollution levels slowly decrease in the lakes due to remedial activities, stocks of fish (like whitefish and perch) and invertebrates (like clams and mussels) have rebounded somewhat.

　　

Lake Ontario

Toronto skyline on the shores of Lake Ontario. Covering 7,340 square miles, Lake Ontario is the smallest of the Great Lakes by surface area but larger than Lake Erie by volume due to having deeper waters. Bordered by the province of Ontario to the north and the state of New York to the south, Lake Ontario’s primary inlet is the Niagara River, which connects to Lake Erie by way of Niagara Falls. The St. Lawrence River is the main outlet of both Lake Ontario and all the Great Lakes into the Atlantic Ocean. The largest city on Lake Ontario (and all the Great Lakes) is Toronto, with a population of just short of 3 million, making it slightly larger than Chicago on Lake Michigan.

　　

Lake Erie

Three Tall Ships sail into Cleveland on Lake Erie during the annual Tall Ships Festival. Editorial credit: Paul Giglia / Shutterstock.com Lake Erie is the second smallest of the Great Lakes in surface area, covering 9,910 square miles, and the southernmost, shallowest, and warmest of the five lakes. The province of Ontario and states of Michigan, Ohio, Pennsylvania, and New York border Lake Erie, and key lakefront cities include Cleveland, Ohio; Toledo, Ohio; Buffalo, New York; and Erie, Pennsylvania. Lake Erie’s primary water source is the Detroit River, and its primary outflow is the Niagara River, although some of the outflow goes through the Welland Canal, which bypasses Niagara Falls. In winter, moisture from the lake can create huge lake-effect snowstorms that impact cities such as Buffalo and Erie on the southern and eastern shores.

　　

Lake Huron

A sunken ship in Lake Huron at Fathom Five National Marine Park, Ontario. The second largest of the Great Lakes, Lake Huron, covers 23,007 square miles and borders the province of Ontario and the state of Michigan. No cities with populations greater than 100,000 border Lake Huron; the largest city is Sarnia, Ontario. Lake Huron connects to Lake Superior via the St. Mary’s River, and its main outflow, the St. Clair River, eventually leads to Lake Erie. Manitoulin Island is the largest island in Lake Huron as well as the largest freshwater island in the world. Technically speaking, because the five-mile wide Straits of Mackinac connect Lake Huron and Lake Michigan, they can be (but usually are not) considered to be one lake.

　　

Lake Michigan

Aerial view of the Holland Harbor Lighthouse at the channel connecting Lake Macatawa with Lake Michigan in the Holland State Park, Michigan. When considered a separate lake, not as a combined lake with Lake Huron, Lake Michigan covers 22,404 square miles and is the only one of the Great Lakes not to border Canada. Instead, the lake’s borders are the states of Michigan, Indiana, Illinois, and Wisconsin. Chicago is the largest city on Lake Michigan and the second largest on the Great Lakes, with a population of about 2.75 million. Lake Michigan (again, when considered as a separate lake) is an outlier compared to the other Great Lakes, which are connected one to the next by a string of rivers; its only Great Lakes connection is with Lake Huron via the Straits of Mackinac.

　　

Lake Superior

Kayaking along Lake Superior Caves near Munising, Michigan. As befitting its name, Lake Superior is the largest of the five Great Lakes (and the largest freshwater lake in the world), registering at roughly the same surface area as the state of South Carolina—31,700 square miles. As the furthest north and east of the lakes, its water flows through Lakes Huron, Erie, and Ontario (and the rivers between them) on its way to the St. Lawrence River and the Atlantic Ocean. Lake Superior is bordered by the province of Ontario and the states of Minnesota, Wisconsin, and Michigan. Important port cities on Lake Superior include Sault St. Marie, Michigan, Thunder Bay, Ontario, and Duluth, Minnesota, the furthest inland ocean port in the world.

　　Covering some 94,250 square miles and holding more than 5,400 cubic miles of water, the five Great Lakes are, by statistics alone, one of Earth’s most impressive natural features. Though a relatively recent addition to the North American landscape, they have had a major impact on the environmental and human history of the continent. It is safe to say that both Canada and the United States would have developed very differently without the presence of the Great Lakes in the heart of North America.