Much of the route between Ameijoeira and the village of Castro laboreiro is accompanied by the river bearing the same name. The Castro Laboreiro River rises in the plateau of Castro Laboreiro, very close to the border with Galicia, running south towards the river Lima which it joins in the middle of the Alto Lindoso reservoir.

It is the principal watercourse in this northwest area of the National Park and largely responsible for the landscape that we find here, separating the Serra da Peneda from the "Montes" of Laboreiro (plateau). It was also a determinant factor in the organisational model adopted in the settlement of Castro Laboreiro, influencing the location of settlements and the network of paths, as well as the construction of numerous bridges that facilitate connections between the margins of Laboreiro.

The Laboreiro is itself an international river, defining, in its lower section, the border between Portugal and Spain, more precisely from border marker post N. º 53 (near the winter settlements of Mareco and Ameijoeira) and to the Alto Lindoso Reservoir, whose waters are also shared by both countries.

As with other montaine watercourses, the Laboreiro River features small natural lagoons containing truly crystalline waters. Throughout its course but especially near the principal population nucleus (Castro Laboreiro), several watermills were built, these are currently unused or have been converted for other uses.

The Laboreiro River and its margins support important biological communities, notably riparian woodlands and their associated faunal species, such as Schrieber’s green lizard, the otter, blackbird and the common carp.