Senia or Sénia may refer to:
The Sénia River is a river in the provinces of Castellón and Tarragona, Spain It begins its course at in the Barranc del Salt, Ports de Beseit limestone massif near La Pobla de Benifassà.
The Sénia flows from west to east marking the historical limits between Catalonia ( Montsià) and the Valencian Community ( Baix Maestrat). It ends its course in the Mediterranean Sea at Sòl de Riu., between Vinaròs and Alcanar municipalities. Its flow is highly irregular. Some years its riverbed remains dry during the whole stretch of its lower course.
The Ulldecona Dam is a dam built across three tributaries of the Sénia river in the Tinença de Benifassà area. With a surface of and a capacity of , its reservoir is very important for the irrigation of fields of the region.