| Cenia | |
| Subdivision Type1: | Country |
| Length: | 50km (30miles) |
| Source1 Elevation: | 1358m (4,455feet) |
| Mouth Elevation: | 0m (00feet) |
| Basin Size: | 197km2 |
The Cenia is a coastal river in Spain that flows through the eastern part of the Iberian Peninsula. Along a significant portion of its course, it acts as a border between the provinces of Castelló and Tarragona. It has a length of 50 km and it flows into the Mediterranean Sea.
The river originates in the Ports de Tortosa-Beseit, within the municipality of La Pobla de Benifassà. The river's waters are accumulated in the Ulldecona dam, also located in the same municipality at an elevation of 477 meters above sea level. This reservoir, with a surface area of 116 hectares and a capacity of 11 hm³, is the only infrastructure regulating the river and is used for irrigation.
From the reservoir, the river passes through areas with steep slopes, which provide it with high oxygenation. Vegetation is abundant in this area, contributing to maintaining the habitat for aquatic life. Further downstream, before reaching the homonymous municipality, water diversions are made to supply irrigation for an area of approximately 2,360 hectares.
Just before the town of La Sénia, the river marks the border between Catalonia and the Valencian Community. From this point until its mouth, the Cenia serves as a border between these two autonomous communities.
As it moves away from this point, the river practically receives no natural contributions, and the water quality deteriorates significantly. Near the town of Alcanar, the river enters the Plana de Vinaroz and crosses this area until it flows into the Mediterranean Sea at Sol de Riu.
This river is described in the sixth volume of the Diccionario geográfico-estadístico-histórico de España y sus posesiones de Ultramar by Pascual Madoz with the following words: