Rend Lake is a 13 miles (20.9 km)-long, 3 miles (4.8 km)-wide southern Illinois reservoir in Franklin and Jefferson Counties near Benton, Illinois. The lake contains 18,900 acres (76 km²) of water, stores 185,000 acre feet (228,000,000 m3) of water, and supplies over 15 million gallons of water per day to 300,000 persons in over 60 communities. The reservoir is up to 35 feet (10.7 m) deep, but its average depth is closer to 9.7 feet (3.0 m). Its elevation is 405 feet (123.4 m) above sea level.
Rend Lake is a reservoir, created when the United States Army Corps of Engineers dammed the Big Muddy River. The dam and lake were authorized in 1962, but the lake was not completely filled until March 1973.
The lakeshore of Rend Lake extends covers 162 miles (261 km), part of which is preserved as Wayne Fitzgerrell State Recreation Area. Swimming beaches at North Marcum and South Sandusky are managed and maintained by the US Army Corps of Engineers. An adjacent Illinois Artisans Shop & Visitors Center is part of the Illinois State Museum system and is operated by the Illinois Department of Natural Resources. (This facility is currently closed due to lack of funding from the state.)
In 2010, Rend Lake was designated as an Important Bird Area of Illinois.