The aim of this thesis is to describe the actual fish ecological status of the river Ager and the river Traun between the lake Traunsee and the confluence with the river Alm. In addition to the fish ecological evaluation using the Fish-Index-Austria, data about fish stocking, piscivorous birds like the cormorant and water temperature records have been analysed. Analysis showed that the good ecological status, which is required in the EU-Water-Framework Directive, can not be achieved throughout the whole investigation area. In the river Traun, this can be ascribed to the low abundance and biomass of the fish stocks, whereas in the river Ager the poor status results from the modified species assemblage like the lack of the nase (Chondrostoma nasus). Regarding temperature conditions, a clear increase of water temperature in the years 1976-2005, especially in the river Ager, has been figured out. The increase results on the one hand from the Climate Change and on the other hand in the river Ager from the local emittents. In some cases, the rising temperatures attain the limit of tolerance of several salmonid species. The maintenance of some for the fishery interesting species like the greyling can only be ensured by massive fish stocking. Other factors, like the increasing appearance of piscivorous birds put additional stress on the fish fauna. The poor fish ecological status of the investigation area along the river Ager and the river Traun results from multiple influences. In total, they cause a decline both in richness and in biomass of the local fish fauna and lead to the disappearance of individual species.