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The Great Waters Program

The Great Lakes

Information provided for informational purposes onlyNote: EPA no longer updates this information, but it may be useful as a reference or resource.
Introduction to the Issues and Ecosystems

The Great Lakes-Superior, Michigan, Huron, Erie, and Ontario-are the largest system of fresh surface water on earth, by area. They contain approximately 18 percent of the world's fresh water supply. Together the lakes contain about 5,500 cubic miles of water covering a total area of 94,000 square miles. These vast inland freshwater seas (which span more than 750 miles from east to west) provide water for consumption, transportation, power production, recreation, and an array of other uses. The Great Lakes basin is currently home to one-tenth of the population of the United States and one-quarter of the population of Canada.

the Great Lakes


Physical Features

  Superior Michigan Huron Erie Ontario

Length (mi) 350 307 206 241 193
Width (MI) 160 118 183 57 53
Average depth (ft) 483 279 195 62 283
Maximum depth (ft) 1,330 923 750 210 802
Volume (mi3) 2,900 1,180 850 116 393
Surface area (mi2) 31,700 22,300 23,000 9,910 7,340
Land drainage area (mi2) 49,300 45,600 51,700 30,140 24,720
Shoreline (MI) 2,726 1,638 3,827 871 712
Retention time (yr) 173 62 21 2.7 7.5
United States (1990) 425,528 10,057,026 1,502,687 10,017,530 2,704,284
Canada (1991) 181,493   191,017 1,857,961 5,446,611

Fish Advisories

PCBs * * * * *
Dioxins         *
Chlordane * *   *  
Mercury * *      

Despite their large size, the Great Lakes are sensitive to the effects of a broad range of environmental pollutants from agricultural and urban runoff, industrial and municipal facilities, spills, and hazardous waste sites. The large surface area of the lakes also makes them vulnerable to direct atmospheric pollutants that fall with snow or rain (wet deposition) and as dust particles (dry deposition) on the lake surface or within the extensive land drainage system.

Although part of a single freshwater system, each lake has different physical characteristics that influence pollutant impacts (see table at left). In volume, Lake Superior is the largest and also the deepest and coldest of the five lakes. Because most of Lake Superior's drainage basin is forested, supports little agriculture, and is sparsely populated, it is believed that relatively few pollutants enter the lake except through airborne transport.

Lake Michigan is the second largest of the lakes and is the only one that lies entirely within the borders of the United States. The drainage area is sparsely populated in the north except for the Green Bay area. Green Bay has one of the most productive fisheries in the Great Lakes region but receives wastes from a large number of pulp and paper facilities. The southern shoreline of Lake Michigan is among the most heavily urbanized of all the lakes; this region, which includes Milwaukee and Chicago, is home to 8 million people.

Huron is the third largest lake by volume. The northern shore surrounding the Georgian Bay is a recreational area for both Canadian and U.S. citizens. The Saginaw River basin is farmed intensively and contains the metropolitan areas of Flint and Saginaw Bay. Like Green Bay, Saginaw Bay contains a highly productive fishery.

Lake Erie is the smallest of the lakes by volume and yet is the most significantly stressed from both urbanization and agriculture. The lake receives agricultural runoff from southwest Ontario and portions of Ohio, Michigan, and Indiana. Seventeen urban areas, each with a population of more than 50,000, are within the drainage basin.

Although slightly smaller in area than Erie, Lake Ontario is much deeper. Major Canadian urban industrial areas include Toronto and Hamilton; however, the US shoreline is less urbanized and not intensively farmed except in the area adjacent to the lake shore. Development in the Great Lakes region has taken advantage of the many resources within the watershed:

  • Agriculture - Grain, dairy and meats, and specialty crops such as fruits, vegetables, and tobacco are produced.

  • Urbanization and industrial growth - The major industries in the Great Lakes basin produce steel, paper, chemicals, automobiles, and a wide array of manufactured goods. Urbanization, accompanied by industrial growth, brought an increase in the number of municipal water and sewage treatment facilities and industrial plants that discharge their effluents into the Lakes.

  • Shipping and transportation - Commodities, primarily iron ore, coal, and grain, are shipped via an extensive navigational system that extends through the St. Lawrence Seaway to the Atlantic Ocean.

  • Commercial fishery - Only pockets remain of a once large commercial fishery for lake trout, lake whitefish, coho and chinook salmon, and walleye. In the US waters, the commercial fishery is based primarily on lake whitefish, smelt, and perch and on the alewife for animal feed.

  • Sport fishery - Today walleye, splake, and coho, Chinook, and pink salmon predominate the sport catch; however, with few exceptions, none of these predator species has been able to reproduce and the fishery has had to be restocked year after year.

  • Recreation - The economy of many areas in the Great Lakes basin depends heavily on tourism and revenues from local recreation- al activities, including sport outfitters, marinas, boatbuilders, resorts, and restaurants.

Water Quality Issues

By the late 1960s, the most obvious problems affecting the Great Lakes were inputs of nutrientsand oxygen-demanding materials, largely from direct piped discharges from municipal wastewater treatment plants and industries. In particular, excess phosphorus led to algal blooms near the
shorelines that interfered with recreational uses and caused taste and odor problems in drinking water. As mats of dead algae settled into bottom waters, oxygen levels plummeted, causing fish kills. Lake Erie was the most vulnerable to these problems due to its shallow depth, warm temperatures, and many wastewater discharges. To a lesser extent, Lake Ontario and natural embayments such as Green Bay and Saginaw Bay experienced similar problems.

Impacts from conventional water pollution were added to decades of cumulative effects from overharvesting of fisheries, the introduction of exotic species, dredging operations in harbors and shipping channels, and habitat alterations in shorelines and wetlands due to agricultural, urban, and industrial development. The harm from conventional pollutants was also made more severe by the widespread use of chemicals such as DDT that accumulate in fish tissues and magnify up the food chain.

By the late 1970s, major investments in upgrading wastewater treatment facilities and the promotion of improved conservation practices in agriculture led to significant progress in controlling conventional waterborne pollutants. However, toxics levels in sediments and fish tissue are still a major issue today. The amounts of mercury and some pesticides in fish flesh have often reached levels serious enough for public health authorities to issue warnings about eating certain sizes and species of fish. In some instances, long-term exposure raises health concerns over cancer. Ongoing research suggests that there are other types of risks, ranging from birth defects to harmful physiological impacts to children. Similar toxicity concerns are also an issue for many types of wildlife.

Concerns over these toxics have encouraged a comprehensive approach to management initiatives in the Great Lakes. This approach starts with the realization that the natural environment cannot be viewed apart from the institutional ecology of human beings and their economic systems. While many management initiatives can best be implemented by focusing on subsystems such as particular Great Lakes or Areas of Concern, these geographically targeted activities must always take into account the fact that the entire Great Lakes basin is interconnected. Such a comprehensive perspective also requires an understanding of the movement of pollutants through air, surface water, sediment, and ground water.

Major Pollution Control Initiatives

In recent years, several major environmental laws have been amended to contain features relevant to Great Waters or specifically to the Great Lakes basin. The 1990 Clean Air Act contains provisions related to water and land ecosystem impacts from the deposition of air pollutants, with particular emphasis on toxics. Under the Superfund and Resource Conservation and Recovery Act (RCRA) programs, the Toxics Release Inventory improves the knowledge base for life-cycle tracking of wastes from industrial processes and encourages recycling and pollution prevention efforts. Ecological risk assessments of the threats posed by waste disposal facilities are becoming more sophisticated, and progress under the Assessment and Remediation of Contaminated Sediments (ARCS) program holds promise of reducing pollution impacts from toxic sediment. Cooperative efforts with other federal agencies such as the U.S. Department of Agriculture, the National Oceanic and Atmospheric Administration, the Fish and Wildlife Service, and the Corps of Engineers address issues as diverse as appropriate disposal of dredge materials, maintaining biodiversity, and protecting habitats for threatened or endangered wildlife species. Perhaps the most ambitious pollution control initiatives seek to implement provisions of the 1978 U.S.-Canada Water Quality Agreement.

Through a combination of treaty arrangements, federal and state laws, enhancements to existing regulations, and consensus-based approaches involving stakeholders from governments,industry groups, and environmental organizations, problems are tackled at several geographiclevels. Site-specific Remedial Action Plans (RAPs) are nearing completion for Areas of Concern,usually at river mouths or harbors where ongoing pollutant loads, combined with cumulative effects dating to the period before 1970, have created the most severe challenges for remediating toxic sediment problems.

The Great Lakes "Airshed" Bands indicate the approximate number of days required for airborne contaminants to be transported to the Great Lakes basin.

At larger regional levels, each lake is scheduled for the development of a Lakewide Management Plan. Special issues facing each lake will be stressed. For instance, coordinated steps to reduce ongoing pollutant loadings will be a central focus of the plans for Lake Michigan or Lake Ontario. For Lake Superior, the largest and most nearly pristine of the Great Lakes, pollution prevention and the goal of virtual elimination of persistent toxic loadings will be a central theme.

To ensure that appropriate criteria are in place for planning and management activities, proposed Great Lakes Water Quality Guidance contains uniform water quality criteria for toxics in the Great Lakes basin. These criteria can then be incorporated into state water quality standards to guide the National Pollutant Discharge Elimination System permitting process (for point source or piped water discharges) and other programs. EPA and the states will seek to achieve water quality standards by the most efficient means by reducing releases from point sources, from nonpoint or diffuse sources, from atmospheric sources, and from contaminated sediments, spills, and waste sites, as appropriate. An effort is currently under way to address nonpoint sources releasing toxics in the basin, with an emphasis on bioaccumulative chemicals identified in the Great Lakes Water Quality Guidance.

Accumulation of PCBs in Great Lakes Food Chain

The nutrients necessary for plant growth (e.g., nitrogen and phosphorus) are found at very low concentrations in most surface waters. In the process of collecting these nutrients, phytoplankton also accumulate certain synthetic chemicals, such as PCBs and pesticides. These may be present in the water at concentrations so low they cannot be measured even by very sensitive instruments. food web

The chemicals, however, biologically accumulate (bioaccumulate) in the organism and become concentrated at levels that are much higher than in the surrounding water. Small fish and zooplankton consume vast quantities of phytoplankton. In doing so, any toxic chemicals accumulated by the phytoplankton are further concentrated in their bodies. These concentrations are increased at each level in the food chain. This process of increasing pollutant concentration through the food chain is called biomagnification. The top predators in a food chain, such as lake trout, coho and chinook salmon, and fish-eating gulls, herons, and bald eagles, may accumulate concentrations of a toxic chemical high enough to cause serious deformities or death or to impair their ability to reproduce. The concentration of some chemicals in the fatty tissues of top predators can be millions of times higher than the concentration in the surrounding water. Eggs of fish-eating birds often contain some of the highest concentrations of toxic chemicals. Thus, the first apparent effects of a toxic chemical in a lake may be unhatched eggs or dead or malformed chicks. Scientists monitor colonies of gulls and other aquatic birds because these effects can serve as early warning signs of a growing toxic chemical problem. Biomagnification of pollutants in the food chain is also a significant concern for human health. To protect their residents from these risks, all the Great Lakes states have issued fish consumption advisories or warnings about eating certain types of fish.

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