Abstract <p>This study made it possible to reveal microparticles with a higher activity of artificial radionuclides (⁶⁰Co, ¹³⁷Cs, ¹⁵⁴Eu, and ²⁴¹Am) in bottom sediments (BSs) of the Yenisei River, in the area affected by the operation of the Rosatom Mining and Chemical Combine. For the first time, radioactive microparticles were detected in BSs collected from three river areas, while about 25 years ago, microparticles were found in one river area only. In terms of their radionuclide composition, these microparticles are divided into mononuclides and polynuclides. The contribution of ¹³⁷Cs, ¹⁵⁴Eu, and ⁶⁰Co contained in the microparticles to the total activity in BSs varies from 81 to 95%, thus exceeding the values earlier reported on microparticles from floodplain soils and BSs. ²⁴¹Am is included in both microparticle groups and demonstrates the highest contribution as Am-microparticles to the total activity in BSs in all study areas (up to 99.6%). The presence of microparticles in the Yenisei River floodplain causes the nonuniform radionuclide distribution over the area and makes it difficult to assess the total radionuclide contamination level in the river floodplain and the mobility of radionuclides in the ecosystem.</p>