The river is 56 km long and flows through the municipalities of Inicio, Puebla del Brollón, Monforte de Lemos, Pantón and Sober, Lugo.

The fish that inhabit the river are the trout, family of the Salmonidae, the bog Leporinus obtusidens, the common carp Cyprinus carpio and some "black-bass", Micropterus salmoides floridanus, fish introduced into North American rivers called black perch.

The river begins in a place called "Fonte das Abellas", near the village of Cabude, the parish of Foilebar, in the municipality of Inicio.

It begins at the Saa River and enters the concello of Monforte de Lemos and flows through the villages of A Parte, O Freixo, Ribas Altas where it joins with the Mao river and enters the capital of Monfortina where it crosses a medieval bridge.

It serves as a boundary between the concellos of Panton and Sober, Lugo, showering the parishes of Canaval, Vilaescura, Rosende e Anllo, of Sober, and Mañente, Vilamelle, Espasante, Cangas, Acedre and Frontón, of Pantón.