The Masma is a worthy representative of the rivers of the Galician Cantabrian slope. A short course (46.2 km),
which begins at an altitude of 900 metres and whose erosive power results in wide valleys like the Mondoñedo
valley; indigenous plant life amongst forests produced by reforestation; and finally, the formation of high
estuaries accompanied at their mouth by inter-tidal plains, is surrounded by mud flats. In the case of the Ría de
Foz, it is closed in by the beaches of A Rapadoira, on the left bank, and the beach of O Altar, on the right. The
estuary is an internationally famous migratory and resting point for birds.
There are many routes along the river, one of Galicia’s best salmon streams. One of the best is that of Pena
Cornería (437m), although you need to be in good shape to make the ascent on foot. The reward is in the
landscape, with panoramic views of the whole Marina coast. There are other accessible lookouts, such as the
peak of A Lebre (Foz), and recreation areas, like that of Fervenza (Viloalle) with artificial river swimming pools
in a tributary of the Masma, close to Mondoñedo.