Lake Monona forms the isthmus's south shore. It is a freshwater drainage lake in Dane County, surrounded on three sides by the city of Madison and on the southeast by the city of Monona, and it forms the south shore of the isthmus that creates downtown Madison. The name 'Monona' is believed to mean 'beautiful', though the Ho-Chunk originally called it 'Tchee-ho-bo-kee-xa-te-la' or 'Teepee Lake.' Lake Monona rests at 43°4′9″N 89°21′34″W, measures 3,274 acres, with a mean depth of 27 feet and a maximum depth of 74 feet.
It holds roughly 28 billion US gallons, and its 13 miles of shoreline are about 40 percent publicly owned. The lake sits at an elevation of 845 feet, its level regulated by locks at the mouth of the Yahara River at Lake Mendota. Three tributaries feed it — the Yahara River from Mendota, Starkweather Creek, and Wingra Creek — and it is the second-largest in a chain of four lakes along the Yahara River with Mendota, Kegonsa, and Waubesa.
Typically it freezes about 107 days a year, give or take 10 days. Water here freezes about 107 days a year, give or take 10 days.