Chew Valley Lake is in the Chew Valley at the northern edge of the Mendip Hills, surrounded by meadows and woods and close to the villages of Chew Stoke, Chew Magna and Bishop Sutton. When it was built in the 1950s, its 1,200 acres (4.9 km²) were flooded with 4,500 million imperial gallons (20,000,000 m³) of water from the Mendip hills, with a catchment area of 14,000 acres (57 km²). It is shallow, with an average depth of 14 ft (4 m) at top level and a maximum depth of just 37 ft (11 m). It is fed by small rivers, and it flows into the River Chew for 17 miles (27 km) before it joins the Avon to head out to sea. The deepest part is near the dam and the outlet tower, where the steeply sloping shores of Walley Bank and the north shore result in depths of up to 20 ft (6 m). "Denny Island", above the surface throughout the year, is wooded and provides a habitat for wildlife.