A representative number of 11 inland waterways of the north-eastern lowlands in Germany was surveyed between 1992 and 1994 using different ®shing methods. Data were pooled for sites and waterways. From the 234 sites investigated, a total of 53432 ®sh were collected and 29 species recorded. The typical ®sh assemblage of the waterways was subdivided into three de®ned classes according to presence and relative abundance of species: reference, accompanying and minor species. The ®sh fauna was characterized by the dominance of roach (Rutilus rutilus) and perch (Perca ¯uviatilis). Both ®sh species showed a mean abundance of 70Á61 % (SD 10Á91 %), whereas more than half of the species recorded had a relative abundance <1 %. Two trends could be identi®ed in the ®sh assemblage owing to human in¯uences: an increase in the dominance of roach and perch and a decrease in species number. In particular, intolerant ®sh with a preference for sand or gravel substrata and current diversity have become rare and endangered. The typical ®sh assemblage of waterways in the lowlands differed from that in the uplands with respect to the higher abundance of rheophilic lithophils in the uplands.