The construction of artificial reservoirs is growing due to the increasing agriculture activities, flood/drought events and energy needs. Reservoirs have usually socioeconomic benefits, but negative environmental effects are usually pointed out by those opposing to the construction. In this context, integrated assessment of catchment functioning with and without reservoirs is essential to quantify their effect as stressors of ecological systems. Modeling is essential to allow multiple stressors scenario assessment. This work is embedded into the FP7 project MARS, and its objectives are to implement and improve an integrated modeling approach (watershed and reservoir models) for characterization of the river basin, to improve a reservoir model to simulate the ecological processes in the reservoir, and to simulate the basin/reservoir under different scenarios of water scarcity combined with nutrient loads. The models implemented are the MOHID Land and MOHID Water. MOHID Land will simulate the Sorraia watershed, located in Portugal and the MOHID Water model will simulate the reservoirs Montargil and Maranhão. These models coupled can simulate the processes and scenarios needed to achieve the objectives of this work.