It is the area that lies between two of Galicia’s most significant water courses, both interms of their volume of water and of the wealth of fauna, flora, landscape and culture they hold: the Ulla-Deza River System, which marks the southern boundary, and the River Tambre and its tributaries, which form its northern limit.

The second river basin in importance in this area is the River Tambre (1531 km² ). It has a total length of 124.5 km and two notable tributaries: the Dubra (15 km) and, above all, the Lengüelle (27 km). It has a total length of 124.5 km and two notable tributaries: the Dubra (15 km) and, above all, the Lengüelle (27 km). The River Tambre and its tributaries are home to populations of trout (Salmo trutta) and one particular carp, the chub (Leuciscus cephalus).