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Basic Information

Map of the Great Lakes

Geography & Hydrology

The Great Lakes - Superior, Michigan, Huron, Erie and Ontario - are a dominant part of the physical and cultural heritage of North America.

Shared with Canada and spanning more than 750 miles (1,200 kilometers) from west to east, these vast inland freshwater seas provide water for consumption, transportation, power, recreation and a host of other uses.

The Great Lakes are the largest surface freshwater system on the Earth. Only the polar ice caps contain more fresh water.

Lake descriptions

Lake Erie

Lake Huron

Lake Michigan

Lake Ontario

Lake Superior

Great Lakes Basin

The Great Lakes Basin - the watershed for each lake is in a different color.

Detail: Northeast portion of fhe Great Lakes Basin

The Great Lakes basin is defined by science, engineering and politics.

  1. Most of the basin is defined by hydrology; watersheds that drain into the Great Lakes and their connecting channels are in the Great Lakes basin. See larger version of the map.
  2. A combination of engineering and politics (Canadian) have resulted in the Rideau exception being included in the Great Lakes basin (the orange striped polygon on the Canadian side of the St. Lawrence River). See detail map of northeast portion of the basin.
  3. The Clean Water Act defines the orange striped polygon on the US side as part of the Great Lakes basin (though hydrologically it drains into the St. Lawrence River). See detail map of northeast portion of the basin.

The boundaries on these two maps are defined by 8-digit Hydrologic Unit Codes (HUC8). These may change slightly as more detailed mapping is completed for these watersheds. The maps also display the counties in the Great Lakes basin.

Environmental Issues

Although the Great Lakes are large, they are sensitive to pollutants. Outflows from the Great Lakes are relatively small (less than 1 percent per year) in comparison with the total volume of water. Pollutants that enter the lakes are retained in the system and become more concentrated with time.

Pollution sources

Protecting the Great Lakes Environment

Multiple government jurisdictions make Great Lakes environmental protection complex.

Great Lakes Interagency Task Force

Managing this shared resource internationally

Great Lakes Legacy Act

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