Composition of animal communities can be shaped by both local and regional processes. Among others, dispersal of organisms links local and regional patterns and determines the similarity of communities at increasing spatial distances. Unique and shared spatial and environmental contributions to fish community composition were calculated for watercourse distances between 49 hydrologically connected lakes in the German lowland area. Variation partitioning indicated a dominant unique effect of spatial predictors on fish community composition, whereas the effects of lake morphometry and productivity were weaker. The spatial effect was attributable to an uneven occurrence of small, littoral fish species found even at the small spatial extension covered here (maximum spatial distance ˜550 km). Distance decay of community similarity was moderate, but significant, if all 31 fish species were considered, but the slope of the decay function became steeper if only 11 small-sized, primarily littoral species were included. These results suggest that fish in European lowland lakes can be considered a metacommunity with limited dispersal along watercourse connections in particular for small-sized species. The analysis supports that for an appropriate evaluation of spatial effects on fish community similarity, reliable estimates of local richness are required which include in particular also rare, small-sized species occurring primarily in littoral areas. Furthermore, watercourse distance is a more reliable approximation than Euclidean distance to the real spatial dimension of fish dispersal.