ABSTRACT. – Environmental drivers shaping beetle assemblages in four rivers of NW Spain affected by hydroelectric power stations. In this work, we studied the environmental drivers that shape the water beetle assemblages in four rivers from NW Spain. We also tested whether hydroelectric power stations have a negative impact on these assemblages. A total of 24931 specimens were collected at 20 sites in eight sampling fields (during years 2001-2002). The fauna was collected with a quantitative Surber net. In addition to habitat and spatial parameters, several physical and chemical variables were measured at each site. The environmental variables were then condensed by means of Principal Component Analysis (PCA). The relationship between species and environmental variables was explored by Canonical Correspondence Analysis (CCA). The assemblage composition was analyzed by a non-metric multidimensional scaling (NMDS), and the differences between groups were tested using the analysis of similarity (ANOSIM) considering two factors, the NMDS grouping and the power station impact. The SIMPER routine was used to verify the species contribution to the dissimilarity. We detected a total of 47 species of Coleoptera belonging to 11 families, 43% of which were Iberian endemics. A Canonical Correspondence Analysis revealed that altitude, distance from source and conductivity were the variables that most influence the studied fauna. Significant differences in the faunal composition were registered in NMDS groups 1 and 2, which were made up of sites belonging to different river basin and lithology. Moreover, differences related to the hydroelectric power stations impact could not be detected due to the experimental design. The SIMPER routine highlighted that Elmis aenea (Müller, 1806), Dupophilus brevis Mulsant & Rey, 1872 and E. rioloides (Kuert, 1890) were the species that most contributed to explain the differences between groups