Lake Winnebago

Lake Winnebago
2006 image from space
Location	Winnebago, Calumet, and Fond du Lac counties, Wisconsin
Coordinates	44°00′N 88°24′W / 44.0°N 88.4°W / 44.0; -88.4Coordinates: 44°00′N 88°24′W / 44.0°N 88.4°W / 44.0; -88.4
Primary inflows	Wolf River, Fox River
Primary outflows	Fox River
Basin countries	United States
Max. length	30 miles (50 km)
Max. width	10 miles (15 km)
Surface area	137,700 acres (215.2 sq mi; 557 km2)
Average depth	15.5 ft (4.7 m)
Max. depth	21 ft (6.4 m)
Surface elevation	about 746 feet (227 m) above sea level
Settlements	Oshkosh, Fond du Lac, Neenah and Menasha

Lake Winnebago is a freshwater lake in the north central United States, located in east central Wisconsin. At 137,700 acres (215 sq mi; 557 km²) it is the largest lake entirely within the state, covering an area of about 30 by 10 miles (50 by 15 km), with 88 miles (142 km) of shoreline, an average depth of 15.5 feet (4.7 m), and a maximum depth of 21 feet (6.4 m). It has many shallow reefs along the west shore, and a drop-off type shoreline on the east. There are several islands along the west shore.

The lake has two primary tributaries, the Wolf and Fox Rivers, which combine at Lake Butte des Morts. The Fox River flows west through Oshkosh and into Lake Winnebago at its west central shore, then flows out at the northwest shore, around Doty Island at Neenah-Menasha to Little Lake Butte des Morts. The river then flows northeast and empties into Green Bay and serves as part of the Fox-Wisconsin Waterway. Lake Winnebago is part of a larger system of lakes in Wisconsin known as the Winnebago Pool.

Cities on its shores include the aforementioned Oshkosh, Neenah, and Menasha, as well as Fond du Lac at the south shore. Municipal drinking water systems serving over 250,000 people draw directly from the lake, including systems serving the cities of Oshkosh, Neenah, Menasha, and Appleton.

The lake is a remnant of Glacial Lake Oshkosh approximately 12,000 years ago. Ice blocked water from entering Lake Michigan at Green Bay, and the glacial lake ponded against ice since it had no outlet.