The paper presents the distribution of water mites (Hydracarina) in the lowland river Pasłęka. The investigations were carried out from 1984 to 1986 at 11 sites. 10,338 specimens belonging to 80 species of Hydracarina were collected. A synecological analysis of the fauna investigated was made, phenology and distribution in the longitudinal and transversal profile of the river were studied. More detailed characteristics were prepared for 10 most numerous species.