Basic Information

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.

84% of North America's surface fresh water
about 21% of the world's supply of surface fresh water
Physical features of the Great Lakes
Great Lakes Atlas
Bathymetry data and maps from NOAA's Great Lakes Environmental Research Laboratory

Lake descriptions

Lake Erie

the smallest by volume
the shallowest
- warms rapidly in the spring and summer
- frequently freezes over in winter
- average depth is only about 62 ft. (19m)
- The western basin (about 20% of the lake), is very shallow with an average depth of 24 ft. (7.4m)
retention time = 2.6 years (a measure based on the volume of water in the lake and the mean rate of outflow)
Most of the area around the lake is urban or agricultural.
17 metropolitan areas with populations over 50,000 within the Lake Erie basin
Significant effects from urban and agricultural runoff
Lake Erie Lakewide Management Plan

Lake Huron

the third largest by volume
vacation homes on the shallow, sandy beaches of Huron and along the rocky shores of Georgian Bay
Saginaw River basin is intensively farmed
Flint and Saginaw-Bay City metropolitan areas.
Saginaw Bay contains a very productive fishery
Physical and environmental features

Lake Michigan

the second largest
the only Great Lake entirely within the United States
variable climate, population density and development
- northern part: colder, less developed, sparsely populated
- southern basin: more temperate, among the most urbanized areas in the Great Lakes system.
Milwaukee and Chicago metropolitan areas have about 8 million people, 20% of the total population of the Great Lakes basin
Green Bay has one of the most productive Great Lakes fisheries but receives the wastes from the world's largest concentration of pulp and paper mills
Lake Michigan Lakewide Management Plan

Lake Ontario

second smallest by volume
average depth 283 ft. (86m)
retention time = 6 years (a measure based on the volume of water in the lake and the mean rate of outflow)
urban industrial centers (Hamilton and Toronto) on the Canadian side
U.S. shore is less urbanized, not intensively farmed
Lake Ontario Lakewide Management Plan

Lake Superior

the largest by volume
the deepest and coldest
retention time = 191 years (a measure based on the volume of water in the lake and the mean rate of outflow)
Most of the Superior basin is forested, with little agriculture because of a cool climate and poor soils.
Sparse population
Relatively few pollutants enter Lake Superior, except through airborne transport
Lake Superior Binational Program

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 encompasses large parts of two nations, the United States and Canada.
Nearly 25% of Canadian agricultural production and 7% of American farm production
Population is more than 30 million people - roughly 10% of the U.S. population and more than 30% of the Canadian population

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

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.
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.
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.

toxic and nutrient pollution
invasive species
habitat degradation

Pollution sources

runoff of soils and farm chemicals from agricultural lands
waste from cities
discharges from industrial areas
eachate from disposal sites
direct atmospheric pollutants that fall as rain, snow, or dust on the lake surface, or exchange as gases with the lake water.

Protecting the Great Lakes Environment

Multiple government jurisdictions make Great Lakes environmental protection complex.

The United States and Canada
US EPA and nine other federal agencies
More than 140 different federal programs for environmental restoration and management
8 states
nearly 40 Tribal Nations
more than half a dozen major metropolitan areas
numerous county and local governments

Great Lakes Interagency Task Force

Established by Executive Order in 2004 <link to the document>
US EPA is lead agency (Great Lakes National Program Office)
Provides strategic direction on federal Great Lakes policy, priorities and programs
EPA works with the Council of Great Lakes Governors and the Great Lakes Cities Initiative on regional collaboration.

Managing this shared resource internationally

1909 Boundary Waters Treaty
1987 Great Lakes Water Quality Agreement (GLWQA)
Great Lakes 5-Year Strategy - developed jointly by EPA and its multi-state, multi-Agency partners provides the agenda for Great Lakes ecosystem management
Lakewide Management Plans for each lake

Great Lakes Legacy Act

Great Lakes Legacy Act of 2002
provides $270 million over five years to
- clean up contaminated sediments from the Great Lakes and
- educate people about contaminated sediments
EPA Great Lakes National Program Office evaluates and funds projects
Priority is given to projects that are:
- Cleaning up contaminated sediment
- Identified in a Remedial Action Plan
- Ready to be implemented
- Using an innovative approach, technology, or technique that may provide greater environmental benefits, or equivalent environmental benefits at a reduced cost
- Include remediation that will start within a year of being funded