The paper presents the evaluation of flood risk in the watershed of the Serafa River – the right tributary of the Vistula. The assessment involved the hydrological calculation and hydrodynamic modeling of wave transformation in the riverbed. The final risk assessment was based on the determination of critical areas, where the largest flood losses occur. It has been shown that proper spatial planning plays an important role in reducing flood-related losses. Moreover, it is necessary to take sustainable actions consisting in delaying the runoff from the watershed by the application of different forms of small retention and infiltration methods.