Assessing the impact of anthropogenic warming on river high flows is essential for adaptation planning. This study evaluates the potential impacts of climate change on high flows in five major river basins in Germany: the Rhine, Danube, Weser, Elbe and Oder. We used a large multimodel ensemble of 70 bias-adjusted and high-resolution Regional Climate Model (RCM) simulations that downscaled Global Climate Models (GCM). The mesoscale Hydrologic Model (mHM) is forced with the climate simulation data to estimate the 90th percentile and annual maxima for streamflow in a 30-year period under both historical and future climate scenarios (1.5K, 2.0K and 3.0K warming levels). The study also analyzed seasonal variations in streamflow by separating the summer and winter half-year. We identified an overall increase in high flow (15-30\% for the northern Elbe and western Oder basins for the 1.5K warming and $\ge$ 30\% for the 3.0K warming in the summer half-year) and annual maximum flow for most river basins. An exception to this is the robust reduction in the annual maximum and high flow flow ($\le$ 30\% for the 3.0K warming scenario) in the Alpine headwaters region. Significant uncertainty exists in the projections, with GCM selection contributing more to this uncertainty than RCM choice, particularly during the summer and at 3.0K global warming. The provision of this large bias-adjusted climate model ensemble representing a fine river network can further facilitate the provision of reliable local information for the planning of local adaptation measures.