Reservoir V-11 closing the Techa River Cascade of reservoirs (industrial reservoir of Mayak PA, Ozyorsk, Russia) was investigated. The complex estimation of the V-11 ecosystem state was spent in the summer 2007 and included hydrochemical, radiochemical and hydrobiological researches. Hydrobiological researches included studying of specific structure of the major hydrocoles ecological groups (phytoplankton, macro vegetation, zooplankton, zoobenthos); biotesting of water and sediments; cytogenetic researches of fish blood; definition of phytoplankton radiosensitivity. The maintenance of the core radionuclides in water of V-11 was the following: 90Sr 1.2-1.7 KBq/1, 137Cs 0.6-1.3 Bq/1; in sediments specific activity 90Sr was in limits from 230 to 370 kBq/kg, and 137Cs from 10 to 160 kBq/kg. Excess of maximum limit concentration for water of fishing reservoirs under the SO42 maintenance (excess in 5-7 times) was observed. The specific and spatial hydrobiocenosis structure of V-11 was typical for flat river water basins. At present time V-11 ecosystem is not revealed signs of degradation. As a whole, the ecosystem condition can be characterized as satisfactory. The existing mode of V-11 operation as a reservoir for storage of low-activity radioactive waste is comprehensible from the point of view of reservoir ecosystem state.
