The objective of this study is the research of the fish pass Wien Freudenau with respect to the expected stream channel incision and the calculation of the resulting volume of eroded bed load and the costs to refill the eroded bed load. Therefore, the following measurements were carried out in the fish pass in February and March 2015: 1. Geodetic surveys of the whole fish pass by using 123 cross sections. In the process the river bed, the water level and the embankment were measured in each cross section. 2. Measurement and analysis of the flow velocity in selected locations in the fish pass Freudenau. 3. Examination of the bed load concerning grain-size composition, woody debris and river bed stability in the fish pass. After the collection of the geodetic data in the fish pass, the Cartesian coordinates were determined, using the software Geosi compared with the coordinates of the geodetic surveys carried out in the fish pass in 1998 and 1999. Thereby, the river bed erosion and the resulted volume of eroded bed load could be calculated for each section in the fish pass. From 1998 to 2015 the mean stream channel incision of the natural bypass channel was 24 cm, compared with 65 cm in the nature-like pool type fish way. However, different river bed erosions were determined in the different sections of the fish pass. In this period of time altogether about 3140 m of bed load were carried from the fish pass into the Danube.