A hydrological model (SWAT) is used to quantify some of the indicators that make up the analysis matrix of a multicriteria decision support system (DSS). The analysis concerns the possible construction of a second, new dam on the Caia catchment in southern Portugal, its connectivity to an existing dam, and the impact of a hypothesized climate change scenario. We describe the definition of the decision criteria for the Caia problem, the linking of a reservoir operation module to SWAT (needed to transform SWAT output into DSS indicator values), an improvement to SWAT's weather generator for the future climate scenario, the data processing and model simulation effort, and the use of various DSS functionalities to analyze the three options (existing dam and reservoir, new dam with reservoir hydraulically connected to the existing one, two reservoirs not hydraulically connected) and the two scenarios (current and future climate). This example of the conjunctive use of a distributed simulation model and a multicriteria DSS illustrates how these tools can interact in providing decision support for a multifaceted water resources management problem.