The Fafião River, or Toco River as it is locally known, is one of the main river courses of the Gerês mountain range, fed by its own springs and the waters that run off from the numerous ravines and temporary watercourses.

Like other rivers and streams of the Gerês mountain range, it has a deeply incised valley with steep rocky slopes. In its deepest sections, like many other streams of the area, there are characteristic natural rock pools ("swimming pools"), much appreciated by tourists for their crystal clear waters. At the end of summer the river level can be very low and may even dry out except in the deepest areas (pools) where water remains throughout the year. In winter, due to the rainfall regime (one of the most extreme in the country), the Fafião River carries a large volume of water which throws itself over rock ledges in noisy and impressive waterfalls. This is one of the most popular rivers for visitors and canyoning enthusiasts.

The Fafião River marks the administrative limits of the parishes of Vilar da Veiga (Terras de Bouro) and Cabril (Montalegre), where are found the respective neighbouring hamlets of Ermida and Fafião whose communities fought each other for several generations over the control of common lands. With backs turned against each other and no understanding concerning the right to use a common land area in the uplands (situated within the administrative limits of Ermida, in Terras de Bouro, but actually used by the community of Fafião), the inhabitants of Ermida burned the deck of the Pigarreira bridge over the Fafião River, so that the community in the neighboring hamlet was then unable to access the right bank of the river by the main path.

After decades of disagreement, the two communities reached an agreement, establishing the limits of the common land for either party. Today they coexist peacefully.

The Pigarreira bridge, which in 2000 still had a wooden deck, was upgraded with a concrete deck as is seen today. Also the forestry track that serves the bridge was later paved, improving mobility within the Park and benefiting in particular local communities.