The rivers of Cantabria are short and rapid, descending steeply because the sea is so close to their source in the Cantabrian Mountains. They flow perpendicular to the coastline, except for the Ebro. They also generally flow year round due to constant rainfall. Nevertheless, the rate of flow is modest (20 m³/s annual average) compared to the other rivers of the Iberian peninsula. The rapidness of their waters, caused by their steep descents, gives them great erosive power, creating the narrow V-shaped valleys characteristic of Green Spain. The environmental condition of the rivers is generally good, although increasing human activity due to rising population in the valleys continues to pose a challenge.

The main rivers of the region, sorted by drainage basin, are:

North Basin (flows into the Cantabrian Sea)

Agüera

Asón

Besaya

Deva

Miera

Nansa

Pas

Saja

Ebro Basin (flows into the Mediterranean Sea)

Híjar

Ebro

Duero Basin (flows into the Atlantic Ocean)

Cantabria is the only autonomous community whose rivers flow into every one of the seas which surround the Iberian Peninsula: The Cantabrian Sea, the Atlantic Ocean and the Mediterranean Sea.