This article describes the impact of land use changes within the Iška River catchment, due to natural or anthropogenic factors, on surface runoff and groundwater status, and consequently on flood risk along the Iška River. Additionally, the impact on the lowering of groundwater level around the water supply facility Brest and its wells, and thus on the functioning of the water supply system, supplying drinking water to Ig and Ljubljana, is presented. The impact of changes in land use and forest overgrowth within the catchment on flood risk and on the connections between surface water and groundwater, which enable the functioning of the water supply facility Brest, were analysed by a combination of hydrological, hydraulic and hydrogeological modelling. Twentyseven scenarios were examined, which, in addition to land use changes, included different precipitation events, climate change scenarios, natural hazards (ice storms, bark beetles), and human interventions (afforestation). The consequences of natural or anthropogenic land use changes can be limited, to some extent, by mitigation measures. However, it should be noted that in the areas protected by the legal regime, restrictions, prohibitions and rules apply that also affect remedial measures. Therefore, the water flow must be followed. For the individual processes, the source and the level of risk under normal and emergency conditions must be evaluated.