The Vjosa River (Aoös in Greece) is the second largest river basin of Albania and one of the main transboundary wild rivers in Europe. Actually, the Vjosa river basin, widely known for its beautiful landscapes and ecological values, offers an important national economic growth potential, coming mostly from the tourism sector. Vjosa River basin has no water management or hydrological model, nor a proper integrated management plan. Therefore, in 2016, a project under the framework of the EU Flood Protection Infrastructure Project (FPIP) was implemented at IGEWE. The main purpose was the development of an integrated hydrological and water management model for the Vjosa Basin to identify key vulnerabilities to climate change between the years 2015-2050, applying the Water Evaluation and Planning (WEAP) system, by Stockholm Environment Institute (SEI). This paper describes details on the methodology used for the delineation of the Vjosa catchment, as a crucial part of the development of the hydrological model of the Vjosa river. The GIS model builder is introduced, as a first step of the Vjosa river WEAP model development.