In rural development areas small hydroelectric power plants (HPP) are a valuable source of renewable energy; but interaction between a river and its environment is crucial and negative impact of a HPP operation on the environment must be estimated to evaluate these impacts, hydraulic parameters such as velocity, water depth, Froude Number (Fr) and fluctuation of flow regimes were measured and hydro biological indices of water quality (HBI) were calculated in 10 HPP cascade in the Virvyte river. Field experiment on the consequences of HPP turbines’ operation was performed in natural, directly and indirectly impacted regimes. To determine the concentrations of suspended solids (SS), total nitrogen (TN) and total phosphorus (TP), water samples were taken from each dam both upstream (reservoir) and downstream (river). To predict sedimentation and selfpurification processes in the riverbed and in the flooded valley the mathematical-hydraulic modelling was used. It was established that all the HPP, where water flowed via the reservoirs and downstream through the HPP turbines, changed the natural regimes of SS. All the reservoirs trapped most SS including the finest ones. As a result, in the reservoir bed substrates the percentage of the particles with diameters < 0.01 mm increased about threefold in comparison to that in the river bed. The direct correlation with the coefficients ranging from 0.35 to 0.94 was found between the reservoir capacities and the deposited amounts of these particles. The concentrations of SS were established to decrease due to water retention in the reservoirs. The TN and TP concentrations decreased some more than 10 % when the water stayed in the pond cascades. It was established, that even small dams and reservoirs of HPP may impact change in the environment through facility operations over a sustained period, because in pounded reaches nearby/above HPP dams in the Virvyte river low Fr number in habitats (0.04>Fr> 0.0007) was determined. Fine silt and clay particles rich in nutrients retention and self-purification of the riv