Great Lakes Fact Sheet

The Great Lakes contain about 23,000 km³ (5,500 cu.mi.) of water, covering a total area of 244,000 km² (94,000 sq. mi.) The Great Lakes are the largest system of fresh, surface water on Earth, containing roughly 21 percent of the world supply and 84 percent of North America's supply. Only the polar ice caps contain more fresh water.

In spite of their large size, the Great Lakes are sensitive to the effects of a wide range of pollutants. The sources of pollution include the runoff of soils and farm chemicals from agricultural lands, the waste from cities, discharges from industrial areas and leachate from disposal sites. The large surface area of the lakes also makes them vulnerable to direct atmospheric pollutants that fall as rain, snow, or dust on the lake surface, or exchange as gases with the lake water.


		Great Lake					Totals
Feature	Units	Superior	Michigan	Huron	Erie	Ontario
Average Depth^a	feet	483	279	195	62	283
	meters	147	85	59	19	86
Maximum Depth^a	feet	1,332	925	750	210	802
	meters	406	282	229	64	244
Volume^a	miles³	2,900	1,180	850	116	393	5,439
	km³	12,100	4,920	3,540	484	1,640	22,684
Water Area	miles²	31,700	22,300	23,000	9,910	7,340	94,250
	km²	82,100	57,800	59,600	25,700	18,960	244,160
Land Drainage Area^b	miles²	49,300	45,600	51,700	30,140	24,720	201,460
	km²	127,700	118,000	134,100	78,000	64,030	521,830
Shoreline Length^c	miles	2,726	1,638	3,827	871	712	10,210^d
	km	4,385	2,633	6,157	1,402	1,146	17,017^d

Population:	U.S. 1990	425,548	10,057,026	1,502,687	10,017,530	2,704,284	24,707,075
	Canada 1991	181,573		1,191,467	1,664,639	5,446,611	8,484,290
Totals:		607,121	10,057,026	2,694,154	11,682,169	8,150,895	33,191,365

Retention Time	years	191	99	22	2.6	6

^Notes: a Measured at Low Water Datum.^b Land Drainage Area for Lake Huron includes St. Marys River. Lake Erie includes the St. Clair-Detroit system. Lake Ontario includes the Niagara River.^c Including islands. ^d These totals are greater than the sum of the shoreline length for the lakes because they include the connecting channels (excluding the St. Lawrence River). Source: Great Lakes Atlas

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 - whether by direct discharge along the shores, through tributaries, from land use or from the atmosphere - are retained in the system and become more concentrated with time. Also, pollutants remain in the system because of resuspension (or mixing back into the water) of sediment and cycling through biological food chains.

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 bathymetric map].

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 bathymetric map].

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 bathymetric map].

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 bathymetric map].

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 bathymetric map].

See the Great Lakes Atlas for much more information on the Great Lakes, their setting, people, environment, and management.