major reservoir for Sydney, east-central New South Wales, Australia. The lake fills the Burragorang Valley, a gorge carved by the Coxs and Wollondilly rivers, which merge there to form the Warragamba, a tributary of the Hawkesbury. With a surface area of about 34 square miles (88 square km) and an average depth of 76 feet (23 m), the lake holds 1,696,000 acre-feet (2,092,000,000 cubic m) of water. It is contained behind Warragamba Dam (completed 1960), which lies 15 miles (24 km) upstream from Penrith and 20 miles (32 km) west of Sydney. The dam is 449 feet (137 m) high and 1,152 feet (351 m) along its crest. The lake also serves to produce hydroelectricity and control floods.