Chagan Lake formed by nuclear explosion. Explosion of the underground nuclear device that was detonated in 1965 to create the crater that became Chagan Lake. This was an example of the Soviet use of peaceful nuclear explosions (PNEs) for earth-moving purposes as part of its Nuclear Explosions for the National Economy programme. The yield of the explosion was equivalent to 140 kilotons of TNT. The site was a dry bed of the Chagan River (a tributary of the Irtysh River) at the edge of the Semipalatinsk Test Site in what is now Kazakhstan. The resultant lake has a diameter of 408 metres and is 100 metres deep. Referred to as 'Atomic Lake', the waters are still radioactive. The detonation took place on 15 January 1965.