Abstract <p>A response of zoobenthos communities to technogenic contamination of special industrial reservoirs of the Mayak Production Association is the biodiversity loss within soft zoobenthos (chironomids, oligochaetes, caddisflies, leeches), mainly at the expense of oligochaete species. An increase in the number and biomass of chironomids (at radiation exposure levels of up to 7.8 ± 0.9 mGy/day) and of oligochaetes (at radiation exposure levels of up to 10.0 ± 2.0 mGy/day) was recorded; however, as the radiation exposure increased further, these parameters decreased. Substitution of the zoobenthos community by a monospecific population of chironomids, accompanied by an increase in their number and biomass, was also observed at radiation doses ranging up to 4500 mGy/day.</p>