Big Lake Butte des Morts (/ˌbjuːdəˈmɔər/) is an 8,800-acre (36 km²) lake located in the U.S. state of Wisconsin and is part of the Winnebago Pool (also known as the Winnebago System). The lake is fed by the Fox River in the southwest and the Wolf River draining from Lake Winneconne in the northwest, and drains via the Fox River southeast into Lake Winnebago. The lake is also part of the Butte des Morts region in Winnebago County, Wisconsin. Much of the lake is flooded marshland created by the damming of the Fox River downstream in Menasha in the 19th century, which explains the lake's flat and shallow character (maximum depth is 15 ft). U.S. Highway 41 (US 41) spans the east end of the lake via a bridge and causeway combination.