Transboundary water resources are important sources of freshwater both globally and at a regional scale in many parts of the world. Effective protection and sustainable use of shared water resources should take into account not only the challenges of integrated water resources management but also additional constraints due to political boundaries. In this presentation it is shown that by integrating hydrologic, hydraulic and environmental economy models, the integrated water resources management approach can be better implemented in transboundary river basins. To demonstrate the effectiveness of integrated modelling as a tool for achieving sustainable water resources management, the case of Mesta/Nestos transboundary river catchment shared between Bulgaria and Greece is presented.