Rush Lake (also known as Rush Reservoir) is a shallow saline lake in Tooele County in the U.S. state of Utah. It is a remnant of Lake Bonneville, an ancient postglacial inland sea that covered much of the western United States during the Ice Ages. The lake is a natural impoundment of a stream that drains into the Great Salt Lake. Rush Lake varies in size, evaporating at about 2 feet (0.61 m) per year, although occasional floods refill the lake. The average surface elevation is 4,951 feet (1,509 m).