The importance of hydroelectricity to the world energy grid motivates the implementation of dams and formation of reservoirs. This implies changes in the ecosystem, and therefore those waters must be constantly monitored. Given the relevance of applied scientific research to monitoring data, this study aims at the spatio-temporal characterization of the water quality of Capivari-Cachoeira hydroelectric power plant reservoir located in Southern Brazil, as well as the water supplying it and the water that is restored to the river. Historical monitoring data obtained between 2005 and 2016 were used for the analysis. The factor analysis used for the study of these data resulted in two factors that explain 59.7% of the total variability. The first factor represents the influence of anthropic activities and land use, signaling the existence of polluting sources upstream of the reservoir. The second fator represents seasonality. Kruskal-Wallis tests applied in factor scores and in the variables with higher factor weights resulted in significant spatial and temporal difference. Regarding the first factor, the reservoir station and those located downstream differed spatially from those located upstream. In the reservoir, reduction in concentration of phosphorus and total solids suggests sedimentation, consequently reducing its values downstream. Considering the seasonal factor, the results obtained during winter showed the lowest temperatures and had the highest values of dissolved oxygen, with the exception of the samples from the reservoir. Thus, the control of the nutrient supply in dammed river demonstrated to be an important tool for managing water resources.