The Guadiana is a transboundary basin whose water resources are shared by Spain and Portugal. The river rises in the Spanish province of Cuenca and flows 778km first in a westerly direction, then south into the Gulf of Cadiz near the Portuguese port of Vila Real de Santo António (Figure 6.1). It drains an area of 66,800km2 of which 11,580km2 (17 per cent) lies in Portugal. Within NeWater, work has concentrated on the Spanish side of the basin, although not exclusively.