The industrial activities and human agglomerations generate significant quantities of specific pollutants that reach in the surface water resources and affect their quality. When quantities of pollutants exceed certain limits the natural processes of self-purification cannot take place and so the aquatic and terrestrial environment is affected on the long and very long term. The paper has studied the evolution of the water quality on the Bistrita River, on the section Piatra Neamt - Bacau and the influence of the polluting factors on it. In the paper was taken into account the integrated principle of flowing waters in which the hydrological element is essential. Five sections of monitoring were studied to determine the influence of pollutants on water quality of the river. The Integrated Assessment Method of the punctual pressures impact on water resources shall be applied taking into account the characteristics of the source of pollution in terms of quantity and quality; the impact on the receiver and the risk to human health, the environment impact and economic activities impact. The point sources of pollution taken into account are: domestic pollution sources, industrial and agricultural pollution sources. By applying integrated method resulted that the most important source of pollution in the studied area is the SC APASERV Piatra-Neamt, operator that manages the wastewater generated from the activities in the Piatra-Neamt city. As a result of research conducted was observed at the present Bistrita River has an increase in the quality condition of waters on this section. Have been observed the imbalance situations in aquatic system on this section due to the hydro morphological change given by the functioning of hydroelectric system Piatra-Neamt - Bacau, and the quantities of pollutants discharged from human agglomerations Piatra-Neamt, Bacau and Buhusi, and because of historical pollution and diffuse sources effects.