Lake Karachai, located on the outskirts of the Ural Mountains, was used as a nuclear waste dump by the Soviet Union, especially during the Cold War. The Mayak nuclear complex, constructed in the late 1940s, produced plutonium for the Soviet nuclear weapons program, generating large amounts of radioactive waste. Between 1951 and 1989, more than 5 million cubic meters of contaminated liquid were poured into Lake Karachai, polluting its soil and water. Radioactive dust collected on the lake's shores during dry periods, and in 1967, strong winds carried the equivalent of 600 curies of radioactive particles more than 75 kilometers away, possibly exposing many people in the surrounding area to radiation. To help contain the radioactivity, local officials placed thousands of concrete blocks into the lake, which significantly reduced its size from 45 hectares in the 1950s to 20 hectares by 1991. Later, the facility was converted into a radioactive waste treatment center, but waste was still dumped into the lake at least until the end of the 1990s, partly to prevent the lake from drying up. In 2015, Russia decided to permanently seal the lake with concrete and established a monitoring program to track local radioactivity levels and that of groundwater. Some reports suggest that since the beginning of radioactive waste storage in Lake Karachai, the rate of cancer among workers at the site and local residents has increased by 21%. There have also been reports of a rise in congenital abnormalities and cases of leukemia in the area. These health concerns highlight the long-term risks associated with nuclear waste disposal and the ongoing impact of past environmental contamination.