The present study is part of the MARS project (Managing Aquatic Ecosystems and Water Resources under Multiple Stress) funded by the European Union. The purpose of this thesis is to investigate the drift and stranding risk of larval grayling (Thymallus thymallus, L.) due to the fluctuating water levels from hydropower plants, so called hydropeaking. In Austria, hydropeaking affects approximately 965 km of river stretches. Hydropeaking rivers are inhabited by European grayling (Thymallus thymallus, L.), which are dominant species that has been listed as endangered species in Austria since 1997. The fish is very susceptible to high flow fluctuations, especially in the early life stages due to their preferred habitat and juveniles are rarely found in river sections with significant changes in flows. The ultimate objective of the present thesis is to investigate the influence of the lateral slope of gravel bars and the time of the day on drift and stranding behaviour of graylings due to hydropeaking. Experiments were conducted at the HyTEC (Hydromorphological and Temperature Experimental Channels) facility in Lunz am See (Lower Austria). Hydropeaking simulations and reference experiments were performed during the day and night at 3.5% and 11% lateral gravel bar slope. The graylings used for the trials comprise hatched larvae originating from wild fish from the rivers Ybbs, Salza and Mur. Fish size was between 17.31 mm to 22.40 mm and the age from 4 to 29 days after hatching. The experiments were executed between 06.05.-23.06.2015. The results revealed that the time of the day has a significant influence on the stranding of larval graylings. During the night, more fish stranded compared to the day time. In terms to the lateral gravel bar slopes, more stranding occurred on the 3.5 % than on the 11 % slope, although the difference was not significant. Downstream displacement of larval graylings was not affected by the time of the day or the lateral slopes of gravel bars.