Previous national and international studies on hydropeaking provide insufficient basic information to derive national river basin management plans with regards to the implementation of the European Water Framework Directive. Moreover, high financial losses for the hydroelectric energy sector, for instance, are expected if uniform limits for hydropeaking ratio are prescribed. In an alpine country like Austria its very important to analyse hydropeaking, because 1/3 of the generated hydroelectric energy is provided by storage power stations. Particularly the influence of variable river morphology and river hydraulics and their interaction with hydropeaking havent been analyzed thoroughly enough. This thesis provides the results for the case study of the Ill river in Austria. Accordingly, it contributes to a rivertyp specific evaluation. By hydrodynamic numerical modeling the hydraulic basic data have been derived. The evaluation of 3 different river reaches, which are affected by hydropeaking, was conducted with the Mesohabitat Evaluation Model (MEM). MEM uses the modeling results of the hydrodynamic model as preprocessing and was developed by the Institute of Water Management, Hydrology and Hydraulic Engineering of the University of Natural Resources and Life Sciences in Vienna. Furthermore, an additional monitoring of the water temperature was performed to study possible changes in water temperature caused by hydropeaking processes. It turned out, that equal hydropeaking ratios are able to cause different impacts on various distinctive river reaches in regard to the habitat quality. According to the level of the base flow different impacts on abiotic habitat characteristics in one and the same river reach are possible. Moreover as limiting factors the river regulation and the high base flow, especially in summer, have to mentioned. Additional, the stability of the spawning grounds could be basically affected by hydropeaking. An influence on the water temperature was not detected throughout the monitoring period (autumn, winter).