The fluvial river basin of the river Sella has a length of 1200 Km2. The river sella draws for cross-sectional limestone and cordales masses in the passage that takes to him from the Source of Hell to its opening in Ribadesella, of 1300 mtrs of altitude at the level of the sea in 73 km.

The river sella is born on the foot of the Stop of the Ponton (1290 mtrs), in the call Source of Hell, next to this Stop appear the tips: the Rocha, Jario, Pozúa, Rock Dwell and the Crest of the Niajo.

By the Defile of the Beyos (12 km), between the rocks Frailón and Monxines, Sella by this so narrow throat passes that “it makes” disappear to Sella. More down, the left slope this presided over by the Cetín Speck, that divides the river basins of Sella and Piloña, to its right the mountain range of Vis and Amieva, conforming a spectacular valley. In the average zone, we found the Hill of Fayes, from which one descries to Arriondas and all the average river basin of the river. From Corona of the Castiello (left) and the Tip Corona (right) we can descry the confluence of the Sella river with the Bay of Biscay.