With a catchment area of 77 km2, it is considered one of the least polluted rivers in Europe. Born in the mountains of Leomil, which starts a journey of approximately 112 km, running through the municipalities of Castro Daire, S. Pedro do Sul, Arouca, Castelo de Paiva and Cinfães (in the territory of Montanhas Mágicas®), it flows into the Douro River between Castelo de Paiva and Cinfães. Here we find a small island called “Ilha do Castelo” (Castle Island) or “Ilha dos Amores” (Love Island), the only one that exists throughout the national section of the Douro River.

In its riverbed and banks there is a great species diversity of fauna and flora, as well as species of priority habitats. Its vegetation is relatively well preserved and includes alders and willows, it is often bordered by oak woods of roble oaks. It is a passage area for the Iberian wolf and covers an important area for the conservation of the mole-of-water, otter, mussel-of-river-loons and blackbird-of-water. It provides conditions for sports like rafting, kayaking and canoeing, it has the best white waters rafting track in Portugal.

Total classified area: 14.562ha

Classified area in the territory: 10.215ha (70%)

Municipalities: Castro Daire, S. Pedro do Sul, Arouca, Castelo de Paiva e Cinfães 

Priority fauna: 

Iberian wolf. 

Protected fauna: 

Pyrenean desman; european otter; iberian emerald lizard; gold-striped salamander; freshwater pearl mussel; great capricorn; stag beetle; orange-spotted emerald; northern straight-mouth nase; ray-finned fish;  Iberian frog; Perez’s frog; marbled newt.

Protected flora: 

Mountain arnica; petticoat daffodil; Angel’s Tears; butcher’s-broom; anarrhinum longipedicellatum; centaurea micrantha ssp. Herminii; scilla beirana; common alder; English oak. 

Prioritary habitats: 

Laurus nobilis arborescent thickets, pseudo-steppe with grasses and annuals of the Thero-Brachypodietea, nardus grasslands, rich in species and in siliceous substrates from the mountain areas, Alnus glutinosa and Fraxinus excelsior alluvial forests.