[en] Between 1967 and 1975, the highest levels of radioactive contamination were observed in the northern part of the Caspian Sea and amounted to 100 Bq.m^-3 for ⁹⁰Sr, 19 Bq.m^-3 for ¹³⁷Cs and 11 kBq.m^-3 for tritium. In 1975, the average concentrations of these isotopes in the surface waters of the central and southern parts of the Caspian Sea were 17 Bq.m^-3, 9.6 Bq.m^-3 and 4 kBq.m^-3 respectively. In the period 1967-1975, the ⁹⁰Sr inventory in water of the northern part of the Caspian Sea decreased by 50%, and in the surface layer (0-50 m) of the central and southern parts of the Caspian Sea it decreased by 25%. In the Caspian Sea as a whole, the ⁹⁰Sr inventory over the period of 8 years remained practically the same and in 1975 amounted to 990 TBq. In the northern part of the Caspian Sea, the ¹³⁷Cs/⁹⁰Sr ratio is 0.25. At the same time, the ¹³⁷Cs/⁹⁰Sr ratio practically does not change with depth in the central and southern parts of the Caspian Sea and is, on average, 0.55. (author)