Lake Chagan (or Lake Balapan), Kazakhstan, is a lake created by the Chagan nuclear test fired on January 15, 1965, part of the Nuclear Explosions for the National Economy. Its water comes from the Chagan River (tributary of Irtysh River). Often referred to as "Atomic Lake," the crater lake's volume is approximately 100,000 m3 (81 acre·ft) and the lake is still radioactive. To the south, the rim of the crater holds back the waters of a second reservoir.