Winnebago, Lake, the largest lake in Wisconsin. Some 30 miles (48 km) long and up to 10 miles (16 km) wide, it covers 215 square miles (557 km2) in the east-central part of the state. The Fox River enters the lake at Oshkosh on the west and flows out of it near Appleton on the northwest. Fond du Lac lies on the lake's southern shore. Lake Winnebago is used extensively for recreation.