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
- 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
- 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
- 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
- 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
- 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 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.
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
- 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
- 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