Lake Karachay is a small like 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, form about 1951. This waste had been dumped into the Techa River beforehand. From about 1956, it was also stored in tanks.