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.