The examination of sediment samples collected from the Yenisei River revealed the presence of artificial radionuclides characteristic of radioactive discharges from the MCC facility: isotopes of europium (152Eu, 154Eu, and 155Eu), cesium (137Cs and 134Cs), 60Co,90Sr, and transuranium elements. Radionuclide concentrations in sediment layers remained high as far as 240 km downstream of the MCC. The vertical distribution of radionuclides in sediment cores was very complex, and down-core variations were due to different amounts of radionuclides released by the MCC and due to variations in the hydrologic conditions in the river. Sequential extraction performed on samples of the upper layers of the sediment core showed different degrees of potential environmental availability of artificial radionuclides: the amounts of extracted 90Sr, 152Eu and 241Am were the largest (60–80% of initial activity), then followed 60Co (30%), 238,239,240Pu (15–30%), and, last, 137Cs (5–15%). The distribution of 238U among chemical fractions of sediments was similar to that of 60Co and 238,239,240Pu: 30–40% of 238U initial activity was extracted. In a few samples, 241Am was present in the unextractable form, which may be accounted for by the presence of microparticles of the reactor fuel.