The World War II has changed many things in the world, especially in terms of how the countries protect themselves now. Russia, always competent with America, started actively pursuing the production of nuclear power and weapons at various reactors by the end of the war. They built a secret nuclear facility that used the water from nearby lakes for cooling and dumping wastes. One of those lakes, Lake Karachay, was used so much for dumping radioactive waste by 1990 that just standing beside it would have given you enough radioactive dose to kill you.

Lake Karachay, located in the southern Ural mountains in central Russia, was used as the dumping site for radioactive wastes from Soviet Union’s nuclear weapon facilities, especially Mayak.

Lake Kyzyltash was the largest natural water body capable of providing cooling water for the reactors nearby. However, it soon got contaminated because of the open-cycle system making Lake Karachay, which is much closer to the reactors, a quick dumping site for nuclear waste that was too hot for the underground storage vats. Lake Karachay was originally planned to be used as a storage for extremely energetic materials until they could be returned to the storage vats in Mayak. But, that proved to be impossible because of the immensely lethal levels of radiation and added to that was the 1957 Kyshtym Disaster caused by the explosion of underground vats contaminating the entire Mayak area.

Mayak plant was the first reactor secretly built for the creation of plutonium as a part of Soviet atomic bomb project following the atomic bombings of Hiroshima and Nagasaki by the United States. 

Between 1945 and 1948, the Mayak plant was built with great haste and secrecy. The goal of building the plant was to match the nuclear power of United States and it was given the utmost priority after the atomic bombings in Japan. However, no heed was paid to the safety of workers or how the disposal of nuclear waste was being carried out. The reactors were all optimized to produce plutonium, which meant production of tons of contaminated materials as well. They used an open-cycle cooling system and the water used for cooling the reactors was being contaminated by thousands of gallons every day.

The existence of Mayak was officially revealed in 1990 by which time there was 21 percent increase in cancer cases, 25 percent increase in birth defects, and 41 percent increase in leukemia in the surrounding region. 

Two years after its existence was revealed, Boris Yeltsin, the then Russian president, signed a decree allowing access to western scientists. The lake sediment was estimated to be composed of entirely high-level radioactive waste deposits to a depth of 11 feet and the scientists thought that over 5 million cubic meters of contaminated water had migrated at a rate of 80 meters per year.

In 1990, the waste discharged area emitted 600 röntgens per hour of radiation, enough to give a human a lethal dose if exposed to for just an hour. 

Since the 1960s, the lake had begun to dry up and its area dropped from 0.5 square km in 1951 to 0.15 square km by the end of 1993. In 1968, the area experienced a drought, which caused the dust from the dried lake with 185 PBq to be carried by the wind affecting half a million people. So, between 1978 and 1986, Russian engineers have gradually filled the lake with concrete blocks to prevent airborne contamination. They used over 10,000 hollow concrete blocks to prevent the sediments from shifting. The lake now looks completely filled in with concrete, though still hazardous.

[sources:wikipedia, dailymail]