. The Changing Illinois environment : critical trends : summary report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. Chapter 9 I LAKES AND RESERVOIRS Fish species composition in Lake Michigan has significantly changed. • In the last century one in seven native fish species in Lake Michigan was either extirpated or suffered severe population crashes. Page 63 • Exotics have assumed the roles of major predators and major forage species. Page 63 The uses oflllitiois lakes are varied, from water supply and recreation to
. The Changing Illinois environment : critical trends : summary report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. Chapter 9 I LAKES AND RESERVOIRS Fish species composition in Lake Michigan has significantly changed. • In the last century one in seven native fish species in Lake Michigan was either extirpated or suffered severe population crashes. Page 63 • Exotics have assumed the roles of major predators and major forage species. Page 63 The uses oflllitiois lakes are varied, from water supply and recreation to flood control and cooling water, with most large reservoirs providing at least three of the four. Water supply In the recent geologic past, Illinois was a land of lakes. Today, the largest sun-ivor of that era is Lake Michigan, the sixth largest lake in the world. .Most of Illinois' few other true lakes have glacial origins, being depressions or "kettles" formed in the northeast pan of the state when blocks of ice buried in glacial till melted. A handful of other natural lakes remain in the few natural floodplains of major rivers that created them. .Most Illinois lakes, however, are manmade. They range in scale from huge tlood control reservoirs like Lake Shelbyville to worked-out stone quarries, gravel pits, and farm ponds. In 1991, 70% of the water withdrawn by Illinois public water sup- plies (PWSs) came from lakes. Together, the Cit>- of Chicago and a number of its suburbs withdraw billion gallons each year from Lake .Michigan—more than half of all the water used by PWSs in the state and 75% of all the water drawn from surface Figure 9-1 Amount of Lake Surface Area Impounded During 5-Year Time Periods Since 1880 15,000 < S -. 1880 1900 1920 •) Hectare = acres 1940 1960 1980 ScHircc: Ecologuitl Reioiirccs. Illinois Natural Histor>- Sunty. 1994 sources. Where it is available, groundwater is usually preferred over surface water
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