The variation of water velocity in an artificial dam reservoir is influenced not only by the inflow discharge, but also by the bathymetry of the reservoir and the water level at the dam. The depiction of spatially complex variations in flow velocity through a reservoir would not be possible without the use of hydrodynamic models. A reliable hydrodynamic model of the reservoir is an effective tool for predicting and analyzing changes in the reservoir geoecosystem in an age of changing climate and risk of water stress. A depth-averaged two-dimensional AdH model was used to visualize the hydrodynamics of the Włocławek Reservoir. Running the model for eight different hydrological conditions delivered consistent results and allowed to calibrate the model parameters. Additionally, it provided a way to verify the data regarding the rating curve of the Vistula River upstream the reservoir.