During the period 1979-1989, 50 species of water beetles (Coleoptera) were collected in a sedimentation tank of saline waters, a drainage canal and three sampling sites in the Świnka River. Common freshwater species were dominant, Enochrus bicolor being the only halophile found. Although the numbers of the beetles were small, the qualitative and quantitative structure of their assemblages did not depend on the salinity of water. The most important environmental factors affecting this structure were: water flow, its temperature, spatial structure of habitat, and food resources.