Аннотация:In August 2000, an internatonal expedition participating in the COPERNICUS project "STREAM" explored two floodplain localities on the Yenisei River (Balchug and Kazachinskoe stations) to estimate the contribution of the Mining and Chemical Plant to the radioactive contamination of floodplain landscapes. It has revealed zones of maximum Cs-137 contamination (up to 1000 kBq/m(2)) in the low-level floodplain made up of fine- and very fine-grained sands with loam partings, in the bottom of breachways overlain by thin beds of peaty and in depressions at the back of the medium-level floodplain with sandy silt deposition. The densities of Co-60 and Eu-152,Eu-154 contamination reach their maximum (up to 188 kBq/m(2)) in silty, peaty, and sandy loam parts of the low-level floodplain. Traces of Co-60 and Eu-152,Eu-154 radionuclides were also found in the medium-level floodplain (Balchug station). The high-level floodplain, up to 5.5 m above low-water line, composed of medium- and fine-grained sands is subject to 16-fold Cs-137 contamination against the background. The medium-level floodplain near the Kazachinskoe station, made up of fine-grained sands, is contaminated by Cs-137 at 250-280 kBq/m(2), with the maximum value, 504 kBq/m(2), detected on the barrier beach.