| Saja | |
| Subdivision Type1: | Country |
| Subdivision Name1: | Spain |
| Subdivision Type2: | State |
| Subdivision Name2: | Cantabria |
| Subdivision Type3: | Region |
| Subdivision Name3: | Saja-Nansa |
| Subdivision Type5: | City |
| Subdivision Name5: | Torrelavega |
| Length: | 67km (42miles) |
| Discharge1 Location: | mouth |
| Discharge1 Avg: | 12.1m3/s |
| Source1: | Northern Sierra del Cordel |
| Source1 Location: | Mancomunidad Campoo-Cabuérniga, Cantabria, Spain |
| Source1 Elevation: | 1700m (5,600feet) |
| Mouth: | Ría San Martín de la Arena |
| Mouth Location: | Suances and Miengo, Cantabria, Spain |
| Mouth Elevation: | 0m (00feet) |
| Basin Size: | 442km2 |
| Tributaries Left: | Diablo (river), Navas del Rey |
| Tributaries Right: | Argoza, Bayones, Besaya |
The Saja is a river in the autonomous community of Cantabria, northern Spain. It flows into the Cantabric sea. Part of its course is inside the Saja-Besaya Natural Park
The Saja's source is at 1,700 meters above sea level and it flows rapidly through a steep V-shaped basin during the first kilometers. Past the village of Fresneda the valley starts to open up and it develops a wide alluvial plain in the Cabuerniga valley.
Regarding the ecologic conservation of the river, it is good from the source to the Santa Lucía bridge, from when it begins to show important alterations, and being catalogued as moderately conserved. Down the confluence with the Besaya the alterations are already serious or very serious, being catalogued as badly conserved.[1]