In the article different methodological approaches to estimation of water and bottom deposits quality of the lowland river depending on intensity and types of anthropogenic load are used. According to both water contamination level and contaminants content 3 major zones are distinguished: upper river river mouth region middle flow. Satisfactory convergence of the applied methods in estimating the river ecological state is marked. It's revealed that the river Sok is insignificantly exposed to anthropogenic impact and can be referred to lightly contaminated waterways with relatively satisfactory ecological situation. There's given the ground of marking the reference region of lowland river by integrated indices while monitoring ecological state of the river net in the Middle and Low Volga river basin.

The hydrochemical particulars of the lakes, phytoplankton composition and the chlorophyll content are considered. The trophic status of the lakes is estimated.

Data of long-term observations on the development of the Kuybyshev reservoir ecosystem have been analyzed with the aid of statistical methods. Series of its characteristics with similar rhythm of seasonal, interannual and spatial changes have been established. Correlations calculated with the time-shift showed poor correlation between separate components of plankton, and plankton and benthos. Correlations between phytoplankton, hydrological and hydrochemical characteristics are numerous. Strong correlations have been found in the benthic community.