What are the Great Lakes?

The Great Lakes are five large freshwater lakes on or near the United States-Canada border in central North America: Lakes Superior, Michigan, Huron, Erie, and Ontario, mnemonic HOMES (Huron, Ontario, Michigan, Erie, Superior). Together they hold about 5,439 cubic miles of water, roughly 21 percent of the world's surface fresh water and about 84 percent of North America's surface fresh water, more than any other freshwater system on Earth except for the polar ice sheets. The lakes cover about 94,250 square miles of surface area. They were carved by continental glaciers during the most recent ice ages and formed their present basins as the ice retreated about 14,000 years ago. The lakes drain through the St. Lawrence River to the Atlantic Ocean, with each lake feeding the next in series.

Lake Superior is the westernmost and largest by surface area at 31,700 square miles, the third largest freshwater lake in the world by volume after Lake Baikal and Lake Tanganyika. It borders Minnesota, Wisconsin, Michigan, and the Canadian province of Ontario, and reaches a maximum depth of 1,332 feet. Lake Michigan is the only Great Lake entirely within the United States, bordered by Wisconsin, Illinois, Indiana, and Michigan. It has the third largest surface area at 22,400 square miles. Lake Huron borders Michigan and Ontario, has the second largest surface area at 23,000 square miles, and contains Manitoulin Island, the largest island in any freshwater lake in the world. Lakes Michigan and Huron are connected by the Straits of Mackinac and are technically a single lake by hydrology.

Lake Erie is the southernmost and shallowest, bordering Ohio, Pennsylvania, New York, Michigan, and Ontario, with a surface area of 9,910 square miles and a maximum depth of only 210 feet. Lake Ontario is the smallest and easternmost, bordered by New York and Ontario, with a surface area of 7,340 square miles and a maximum depth of 802 feet. Niagara Falls drops between Lake Erie and Lake Ontario at the international boundary.

Major cities on the Great Lakes include Chicago, Detroit, Cleveland, Buffalo, Milwaukee, Toronto, Hamilton, Mississauga, Toledo, and Rochester. The lakes have been central to American and Canadian commerce since European settlement. The Erie Canal opened October 26, 1825 connected Lake Erie to the Hudson River, opening the interior to Atlantic commerce. The St. Lawrence Seaway opened June 26, 1959 enabled ocean ships to reach Great Lakes ports. The lakes are connected by the Soo Locks at Sault Ste. Marie, the Welland Canal between Erie and Ontario, and the Straits of Mackinac.

About 35 million Americans and Canadians live in the Great Lakes basin. Pollution and invasive species (zebra mussels, sea lampreys, Asian carp) are continuing concerns.