Lake Karachay is a small lake in the Ural Mountains. It lies in Chelyabinsk Oblast, near the town of Ozyorsk.Ozyork was a closed city; the people who worked there built Russia's first nuclear power plant, at Mayak. The lake was used to dump radioactive waste that resulted from operating the Mayak site, from about 1951. This waste had been dumped into the Techa River beforehand. From about 1956, it was also stored in tanks.
The lake is near Mayak, which is the name of a number of nuclear facilities, about 150 kilometres (93 miles) from Ekaterinburg in Russia.