The Great Lakes

The Laurentian Great Lakes were formed nearly 20,000 years ago when the earth's climate warmed and the last glacial continental ice sheet retreated. The glacier, up to 2 miles thick, was so heavy and powerful it gouged out the earth's surface to create the lake basins. Meltwater from the retreating glacier filled the newly created basins. Approximately 3,500-4,000 years ago, the Great Lakes attained their modern levels and area.

Water Volume: 5,500 cubic miles (22,809 cubic km), 90% of U.S. supply, 18% of world supply

Water Surface Area: 95,000 square miles (245,759 square km). Largest surface area of freshwater in the world.

Shoreline Length: 10,210 miles (17,017 km).

Shoreline Use:

• Residential - U.S. 26.5%, Canada 18.6%;
• Commercial / Industrial - U.S. 6.7%, Canada 2.6%;
• Agricultural - U.S. 1.5%, Canada 8.2%;
• Other - U.S. 65.3%, Canada 70.6% (Canada includes transportation/communications, recreation, extraction, water, wetlands, forestry, grassland, barren; U.S. includes public, beaches, forests, barren lands)

Population: 35 million.

Outlets: St. Lawrence River and Chicago Sanitary & Ship Canal

Retention Times (amount of time it takes for lakes to get rid of pollutants):

• Lake Superior: 191 years
• Lake Michigan: 99 years
• Lake Huron: 22 years
• Lake Ontario: 6 years
• Lake Erie: 2.6 years

$4 billion sports fishery industry.

250 species of fish.

Provides drinking water for 40 million people. Provides 56 billion gallons of water per day for municipal, agricultural, and industrial use.

Commercial shipping of 200 million tons over 1,270 mile route.

Provides power generation and cooling water.

Produces 90% of iron ore.

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 have provided water for consumption, transportation, power, recreation and a host of other uses.

The Great Lakes are the largest surface freshwater system on the Earth. They contain about 84 percent of North America's surface fresh water and about 21 percent of the world's supply. Only the polar ice caps contain more fresh water.

• Lake Superior is 1,335 feet deep and 350 miles long. It is the largest of the Great Lakes in both surface area and volume. Lake Superior is the largest in terms of volume. It is also the deepest and coldest of the five. Because of its size, Superior has a retention time of 191 years. Retention time is 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. The forests and sparse population result in relatively few pollutants entering Lake Superior, except through airborne transport. 

Lake Superior Basin Statistics

• Lake Michigan is 925 feet deep and 307 miles long. It is the third largest Great Lake and the sixth largest freshwater lake in the world. Lake Michigan, the second largest, is the only Great Lake entirely within the United States. The northern part is in the colder, less developed upper Great Lakes region. It is sparsely populated, except for the Fox River Valley, which drains into Green Bay. This 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. The more temperate southern basin of Lake Michigan is among the most urbanized areas in the Great Lakes system. It contains the Milwaukee and Chicago metropolitan areas. This region is home to about 8 million people or about one-fifth of the total population of the Great Lakes basin

Lake Michigan Basin Statistics

• Lake Huron is 748 feet deep and 206 miles long. It is the second largest Great Lake and the fifth largest freshwater lake in the world. It has the longest shoreline of the Great Lakes if you count the shorelines of its 30,000 islands. Lake Huron, which includes Georgian Bay, is the third largest of the lakes by volume. Many Canadians and Americans own cottages on the shallow, sandy beaches of Huron and along the rocky shores of Georgian Bay. The Saginaw River basin is intensively farmed and contains the Flint and Saginaw-Bay City metropolitan areas. Saginaw Bay, like Green Bay, contains a very productive fishery

Lake Huron Basin Statistics

• Lake Erie is 210 feet deep and 240 miles long. Lake Erie is the smallest of the lakes in volume and is exposed to the greatest effects from urbanization and agriculture. Because of the fertile soils surrounding the lake, the area is intensively farmed. The lake receives runoff from the agricultural area of southwestern Ontario and parts of Ohio, Indiana and Michigan. Seventeen metropolitan areas with populations over 50,000 are located within the Lake Erie basin. Although the area of the lake is about 26,000 km2 (10,000 square miles), the average depth is only about 19 meters (62 feet). It is the shallowest of the five lakes and therefore warms rapidly in the spring and summer, and frequently freezes over in winter. It also has the shortest retention time of the lakes, 2.6 years. The western basin, comprising about one-fifth of the lake, is very shallow with an average depth of 7.4 meters (24 feet) and a maximum depth of 19 meters (62 feet)

Lake Erie Basin Statistics

• Lake Ontario is 802 feet deep and 193 miles long. Lake Ontario, although slightly smaller in area, is much deeper than its upstream neighbor, Lake Erie, with an average depth of 86 meters (283 feet) and a retention time of about 6 years. Major urban industrial centers, such as Hamilton and Toronto, are located on its shore. The U.S. shore is less urbanized and is not intensively farmed, except for a narrow band along the lake

Lake Ontario Basin Statistics

EPA Great Lakes website

• Great Lakes Shipping

Credit: EPA,NASA