This study was carried out within the frame of the project "Schwallproblematik an Österreichs Fließgewässern - Ökologische Folgen und Sanierungsmöglichkeiten". The project analyses the effects of hydropeaking in Austrian rivers and potential rehabilitation measures. The subject of this thesis is a case study on the River Drau in the federal state Carinthia. The study deals with the impacts of hydropeaking on the development of juvenile grayling. To analyse this issue, habitat use, abundance and size range were analysed in association with the discharge fluctuations. The survey was carried out at six dates between May and October in the year 2009 on the base of the strip-fishing-method in separated habitat types. The strip-fishing-method allows to quantify the stock of juvenile fish. Beside the 0+-age group of grayling, juvenile brown trout and rainbow trout were surveyed. The investigation area was split into a section with hydropeaking influence and a section without hydropeaking influence. The surveyed data of the year 2009 were evaluated statistically and compared with data of previous studies of the Institute of Hydrobiology and Aquatic Ecosystem Management of the University of Natural Resources and Applied Life Sciences, Vienna. Besides the fish stock evaluation, focus was placed on discharge to identifiable impacts of hydropeaking on the juvenile fish stock. The results show that juvenile fish shift their habitats with ongoing development and growth. Moreover juvenile grayling grow faster in the section with hydropeaking influence, compared to the uninfluenced section. Hydropeaking causes a collapse of the juvenile fish stock, when discharge fluctuations increase in September and October. Additionally hydropeaking reduces the reproduction success of brown trout. The thesis highlights the negative impacts of hydropeaking on the juvenile fish stock. For a comprehensive description of the effects of hydropeaking on fish stock development, further studies are necessary.