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The Great Lakes are a group of five large freshwater lakes in North America that are interconnected by natural and artificial channels.
They are (from east to west): Lake Ontario, Lake Erie, Lake Huron, Lake Michigan, and Lake Superior.
Most of them, except Lake Michigan, which lies entirely within the United States, form part of the border between the United States and Canada.
The Great Lakes are bordered by the Canadian province of Ontario and by eight U.S. states including (from west to east) Wisconsin, Minnesota, Illinois, Indiana, Ohio, Michigan, Pennsylvania, and New York. Large cities like Chicago, Detroit, Cleveland, and Toronto lie on the shores of the Great Lakes system.
The Great Lakes system, with a combined surface area of 244,100 sq km, holds about 20 percent of the world's fresh surface water.
Lake elevations decrease to the east and south.
Lake Superior, the largest lake at 82,100 sq km, is also the largest freshwater lake in the world.
Its outlet is the Saint Mary's River, which enters Lake Huron after falling about 7 metres over a series of rapids.
Lake Huron and Lake Michigan lie at the same elevation.
Water flows from Lake Michigan to Lake Huron. Lake Michigan is deeper than Lake Huron, but the latter is larger in area, at 59,600 sq km.
Lake Huron drains into the Saint Clair River, which falls about 3 metres between Lake Huron and the small, shallow basin of Lake Saint Clair. Lake Saint Clair is connected to Lake Erie by the Detroit River.
At its northeast end, Lake Erie empties into the Niagara River, which drops 99 metres as it flows north to Lake Ontario, which is the smallest of the Great Lakes at 19,010 sq km.
Lake Ontario is linked with the Atlantic Ocean via the St. Lawrence River.
The Great Lakes, interconnected by rivers, straits, and canals, are a natural resource of tremendous significance in North America; they serve as the focus of the industrial heartland of the continent and together form one of the world's busiest shipping arteries.
The lakes also form an important recreational resource with about 17,000 km of shoreline, rich sport fisheries, and numerous beaches and marinas.