According to a report by the Washington, D.C.-based Worldwatch Institute on nuclear waste, Karachay is the most polluted (open-air) place on Earth from a radiological point of view. The lake accumulated some 4.44 exabecquerels (EBq) of radioactivity over less than one square mile of water, including 3.6 EBq of caesium-137 and 0.74 EBq of strontium-90. For comparison, the Chernobyl disaster released 0.085 EBq of caesium-137, a much smaller amount and over thousands of square miles. (The total Chernobyl release is estimated between 5 and 12 EBq of radioactivity, however essentially only caesium-134/137 to a lesser extent, strontium-90 contribute to land contamination because the rest is too short-lived). The sediment of the lake bed is estimated to be composed almost entirely of high level radioactive waste deposits to a depth of roughly .