Lake Chagan, also referred to as the Atomic Lake, is a lake in Kazakhstan that was formed by the Chagan underground nuclear test, which was fired on 15 January 1965. The bomb’s yield was equivalent to 140 kilotons of TNT, and was used specifically for earth-moving purposes. Cratering explosives like Chagan release a great deal of steam and pulverized rock and approximately 20% of the bomb’s normal fission products were released into the atmosphere. The crater is 328 feet deep and well over 1,000 feet across. The lake still remains radioactive, although its fission products have decayed to levels that make swimming in it relatively safe.
Note: The second photo is of the lake’s observation deck. In the bottom right corner of the third photo is the same observation deck.