This chapter contributes to assessing the effectiveness of constructed wetlands as flood mitigation measures at catchment scale. The Soil and Water Assessment Tool (SWAT+) was used to model the Råån catchment in southwest Sweden where construction of wetlands has been ongoing since the 1990s. The assessment was based on a paired simulation scenario (with and without wetlands), and performance as nature-based solutions (NbS) was evaluated based on impacts on the downstream river hydrograph (including event-based), descriptive, consequential, and social indicators. The results implied that the flow-regulating capability of the modeled wetlands was directly related to their outflow mechanisms. Because the wetlands seemed to frequently exceed their maximum storage capacity and the excess water was immediately spilled downstream, the wetlands provided limited flood regulation services. However, lack of wetland-specific data motivated a low confidence grade for the indicators. If indicator values are to be useful tools in the future integration of wetlands as NbS, onsite monitoring data and further research are required to assess their impact on upstream-downstream processes.