long artificial lake in Panama, constituting part of the Panama Canal system; its area is 166 square miles (430 square km). It was formed by damming the Chagres River and its smaller affluents at Gatun at the north end of the lake. Its dam (completed 1912) and spillway, a key structure of the Panama Canal, operate at a range of 5 feet (1.5 m) between water levels of 87 and 82 feet (26.5 and 25 m) above sea level. The lake's main function is to hold sufficient water in the Gaillard Cut to the south, a gorge blasted through the Cordillera, for canal passage and for use in the canal's locks during dry spells. In the centre of the lake is Guacha Island, a wildlife sanctuary.