GREAT LAKES

The Great Lakes and their drainage basin. chain of lakes in east-central North America comprising Lakes Superior, Michigan, Huron, Erie, and Ontario. They are one of the great natural features of the continent and of the Earth. Although Lake Baikal in Russia has a larger volume of water, the combined area of the Great Lakes-some 94,850 square miles (245,660 square kilometres)-represents the largest surface of fresh water in the world, covering an area exceeding that of the United Kingdom. Their drainage basin of about 295,800 square miles (which includes the areas of the lakes themselves and their connecting waterways) extends approximately 690 miles from north to south and about 860 miles from Lake Superior in the west to Lake Ontario in the east. Except for Lake Michigan, the lakes provide a natural border between Canada and the United States, a frontier that was stabilized by a boundary-waters treaty of 1909. It is a source of pride for both countries that there are no fortifications or warships along the boundary. Individually, the lakes rank among the 14 largest in the world (see Table). They played a central role in the European colonization and development of North America and for decades have attracted people and industry; Lakes Erie and Ontario and the southern portion of Lake Michigan are now ringed with large population concentrations. The lakes have not benefited from this development, however, and have been seriously affected by pollution. Concern over the fate of the lakes reached a high pitch in the late 20th century, with both the U.S. and the Canadian governments and individuals investigating methods for reversing the consequences of years of misuse of the lakes' waters. The Great Lakes form the western portion of the larger St. Lawrence hydrographic system. This system extends generally eastward from the St. Louis River in Minnesota (which flows into Lake Superior), through the lakes and the St. Lawrence River, and empties into the Atlantic Ocean at the Gulf of St. Lawrence. For a discussion of the system east of Lake Ontario, see Saint Lawrence River and Seaway. chain of lakes in east-central North America comprising Lakes Superior, Michigan, Huron, Erie, and Ontario. The Great Lakes form a natural boundary between the United States and Canada and cover an area of about 94,850 square miles (245,660 square km), constituting the largest freshwater surface in the world. Their drainage basin of about 295,800 square miles (766,100 square km) extends approximately 690 miles (1,110 km) from north to south and about 860 miles (1,400 km) from Lake Superior in the west to Lake Ontario in the east. The Great Lakes are connected to form a single drainage system that discharges down the St. Lawrence River into the Atlantic Ocean. The lakes drain roughly from west to east, and except for Lakes Michigan and Huron (which are at the same elevation), their elevations drop with each lake. The Great Lakes are the end products of glacial activity that began about 1,000,000 years ago during the Pleistocene Epoch (1,600,000 to 10,000 years ago). The modern Great Lakes are situated in stream valleys that were repeatedly made larger by glacial activity. The stream valleys were also depressed by the great mass of the glacial ice over the land. The present Great Lakes are the last stage of a sequence of many lakes in the region dating back to late Pleistocene time. Lake Superior, which is bordered by the Canadian province of Ontario and the U.S. states of Minnesota, Wisconsin, and upper Michigan, is the northernmost and westernmost lake and can be considered the headwater of the system. It is the second largest lake in the world (after the Caspian Sea) and the largest and deepest of the Great Lakes (mean depth 487 feet ). It lies at an elevation of 600 feet (183 m) above sea level and discharges into Lake Huron through the St. Marys River. Lake Michigan lies directly south of Lake Superior and is bordered by upper and lower Michigan, Wisconsin, Illinois, and Indiana. The average water level is 579 feet (176 m) above sea level, and its waters flow northward into Lake Huron through the Straits of Mackinac. Lake Huron, which is bounded by Ontario and Michigan, lies at the same elevation as and is slightly larger than Lake Michigan. It drains through the St. Clair River, the shallow basin of Lake St. Clair, and through the Detroit River to Lake Erie. Lake Erie is bordered by Ontario, lower Michigan, Ohio, Pennsylvania, and New York. It is the shallowest of the Great Lakes, with a mean depth of 62 feet (19 m). It lies at an elevation of 570 feet (174 m), and its waters discharge along the Niagara River and make a rapid plunge over Niagara Falls before reaching Lake Ontario. Lake Ontario has the smallest surface area of the system. It lies between Ontario and New York, at an elevation of 245 feet (75 m), and discharges into the St. Lawrence River. The St. Lawrence River flows for about 750 miles (1,200 km) until it empties into the Gulf of St. Lawrence. The industry of the lakes region is highly diversified. Large quantities of iron ore, coal, grain, and manufactured goods are moved annually between lake ports or shipped overseas through the St. Lawrence Seaway. Among the more important industrial developments are large steel mills in Illinois, Indiana, Ohio, and Ontario and the automobile industry centred in the Detroit, Mich., area. The lakes supply water for these and numerous other industries and for bordering municipalities. Commercial fishing was once a major industry on the lakes, but the decline of the more desirable species because of pollution and other factors led to its collapse. Recovery has been slow and partial. The value of the lakes for a broad spectrum of recreational activities is inestimable. Powerboating and sailing have become major activities. Efforts by U.S. and Canadian agencies to overcome pollution problems have made significant progress in Lakes Michigan and Erie. Experimental planting of anadromous fish species such as coho, chinook, and Atlantic salmon was successful, and a major sport fishery has developed around the salmons, lake trout, and rainbow and other true trout species. Many miles of sandy beaches stretch along the lakeshores. Government lands offer camping, picnicking, and park areas for a thriving tourist industry. Additional reading Jack L. Hough, Geology of the Great Lakes (1958), provides information on the lakes' geologic origin. A summary of the physical, chemical, and biological characteristics of the Great Lakes, with an account of early research in the field, is offered in Alfred M. Beeton and David C. Chandler, "The St. Lawrence Great Lakes," in David G. Frey (ed.), Limnology in North America (1963), pp. 535-558. Harlan Hatcher and Erich A. Walter, A Pictorial History of the Great Lakes (1963), surveys early exploration, shipping, and settlement in the region. Useful background information on the region is found in Lee Botts et al., The Great Lakes: An Environmental Atlas and Resource Book (1987); and R.A. Assel et al., Great Lakes Ice Atlas (1983). A history of ecological changes in the basin and their effect on the lakes is presented in William Ashworth, The Late, Great Lakes (1986). Theodora E. Colborn et al., Great Lakes, Great Legacy? (1990), discusses the Great Lakes as an ecosystem, changes in the lakes' environment, and institutional arrangements for dealing with these problems. The region's economic situation is assessed in Federal Reserve Bank of Chicago and Great Lakes Commission, The Great Lakes Economy (1985), a compendium of data on resources and industry, and The Great Lakes Economy: Looking North and South (1991), an interpretive analysis. Noel M. Burns, Erie: The Lake That Survived (1985), discusses the environmental and economic degradation of the lake and its environs and the signs of rehabilitation. Also useful is Great Lakes Science Advisory Board, Report (biennial), which includes summaries of health, societal, and education issues related to pollution and toxic chemicals. Alfred M. Beeton