Lake Winnebago is a 137,700-acre (55,700 ha; 215.2 sq mi) freshwater lake in eastern Wisconsin, United States. It is the largest lake entirely within the state, covering an area of about 30 by 10 miles (48 by 16 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.