The rostrum dace is a rheophilous Cyprinid fish endemic to some French catchments. Particularly vulnerable to its habitat degradation, the rostrum dace appears to be a patrimonial species. Morphometric features were used to identify populations in a heavily impounded river, the Viaur River. A total of 176 fish, spread over 7 stations, were photographed and then released. A linear discriminant analysis correctly classified more than 80% of the individuals. Significant relationships were found between the morphological differences and (i) the geographical distance, and (ii) the number of artificial barriers (i.e. dams and weirs) between the stations. These results show that discrete dace morphological units occur in the Viaur River and therefore suggest a fragmentation of the population. Although further investigations (e.g. genetics, life history traits, etc.) are necessary to refine these results, conservation measures should be undertaken to preserve this endemic species in the Viaur River.