Lake Tana is the largest natural reservoir in Ethiopia. The Lake sub basin is endowed with good potentials of water and land resources. However, there is a lack of appropriate water resources systems planning and management tools. In view of this an attempt is made to conceptualize the sub basin's water resources systems problems in a simplified way by using a hypothetical equivalent catchment. Simulating the Lake mass balance using the synthetic generated net supply series helps to know the performance measuring indices of the Lake.
