In summer 2015, the distribution of structural indicators of phytoplankton and the macrophytes overgrowth in the Shardara Reservoir's water independent of external factors was studied. Phytoplankton was represented by 78 species; green algae dominated. The abundance of community was 544.0 mln. cells m-3, with biomass at 626.1 mg m-3. Macrophytes Potamogeton natans L. and Potamogeton malajanus L. massively developed on the eastern shallow parts and in bays of the southwestern part of the reservoir. Our research showed that the biotopes inhabited by macrophytes were generally characterized by relatively higher concentrations of nitrite, phosphate, and zinc. The structure of phytoplankton was dependent on many factors, among which the most important were the water temperature and heavy metals. The warm-water status of the Shardara Reservoir was reflected in the dominance of green algae and dinoflagellates. With relatively high concentrations of heavy metals in the ecosystem, their impact on phytoplankton was neutralized by the complex nature of pollution, which included the increased number of organic substances. The impact of toxicants was not traced when analyzing the diversity and abundance of phytoplankton. The prevalence of facultative heterotrophs among the diatoms served as an indirect indication of the presence of toxic substances in the ecosystem. The dimensional structure of phytoplankton changed under the influence of cadmium in size reduction, and that may be the adaptive restructuring of the community in response to the toxic stress. Therefore, we may emphasize the essential indicative importance of size parameters of communities, including the Clarke's W-statistics and Δ-Shannon-Weaver
