Chew Valley Lake () is a big reservoir in the Chew Valley, Somerset, England, and the fifth-largest artificial lake in the United Kingdom (the largest in south-west England), with an area of 1,200 acres (4.9 km²). The lake, created in the early 1950s and opened by Queen Elizabeth II in 1956, provides much of the drinking water for the city of Bristol and surrounding area, taking its supply from the Mendip Hills. Some of the water from the lake is used to maintain the flow in the River Chew.