The species composition and structure of fish communities were studied in 15 sampling areasof the most important rivers of the K r s drainage system. In the paper, our results are compared withrecent literature data on the same waterflows. The fish community was sampled twice in each samplingarea, on 16-25 August 2011 and between 25 June and 11 July 2012, using electric fishing gear accordingto the WFD protocol. The occurrence of a total of 49 fish species was confirmed in the 17 sampling areasof the six rivers, the number of indigenous species was 41. No new species was found in the studiedreaches compared to the recent data. We proved the occurrence of 41 species in the CrisulRepede/Sebes-K r s, 31 species in the Crisul Negru/Fekete-K r s, 29 species in the Crisul Alb/Fehér-K r s, 18 species in one reach of the Kett s-K r s and 16 species in one reach of the Hármas-K r sriver. The most frequent fish species was Squalius cephalus, other frequent species were Alburnusalburnus, Rutilus rutilus, Rhodeus amarus, Alburnoides bipunctatus, Barbus barbus and Carassius gibelio.Of the 15 sampling areas, those of K r sladány and K r sszakál (Sebes-K r s), Ineu (Crisul Alb) andTinca (Crisul Negru) were found to be rich in species (20-22 species). The species richness of the Salistede Vascau (Crisul Negru) sampling areas is well below the average (14.5). The differences between therivers in their species richness can be explained partly with the differences in their habitat structure (fastor slow waterflow, silty, sandy or gravelly bottom), partly with water pollution and hydraulic constructions(water barrages, spillover dams).