The Yahara chain of lakes resulted from glacial action about 40,000 years ago. A massive ice sheet, ? mile thick at Madison, gouged hills and widened valleys as it moved inexorably westward. Changing climate caused the glacier to retreat leaving behind great masses of rock and debris. Blockage in the channel of the pre-glacial Yahara River formed the four lakes, Mendota, Monona, Waubesa, and Kegonsa.
Largest of the four, Mendota's surface covers 15.2 square miles. Its greatest depth is 84 ft. and average depth is 40 ft.
Before the white man came numerous Winnebago Indian villages and camps occupied Mendota's shores. About 350 effigy mounds built by the Winnebago have been identified around Lake Mendota — 1000 in the four lakes area. A bird effigy on the Mendota hospital grounds is one of the finest and has a wing spread of 624 ft.
The Winnebago called the Four Lakes Region Tay-cho-pe-ra. They called Lake Mendota Wonk-shek-ho-mik-la. In 1849 a Madison surveyor, Frank Hudson, gave Mendota its official name after the Sioux Indian term meaning "mouth of the river."