The aim of this work is to provide better understanding of the main physical processes and aquatic ecosystem behavior of Mediterranean Reservoirs caused by natural and artificial perturbations. This book enhances special emphasis of ecological response by combining hydrodynamic and water quality models to two reservoirs located in the region of Catalonia and used for water supply purposes. Investigators, Engineers and students of environmental sciences, limnology and hydraulic engineering might benefit from this small acquired experience in modeling of theses medium-sized reservoirs and subsequently getting a significant help to the water management authority in their decision making. Book, starting with an introduction, data analysis and field experiments, checking criteria for using the 1D hydrodynamic model for the two reservoirs, applying the DYRESM-CAEDYM to the Sau Reservoir, and finally trying to use the same models to another reservoir which is Boadella