Of the roughly 1,800 rivers and streams in Spain, only the Tagus is more than 960 kilometers long; all but 90 extend less than 96 kilometers. These shorter rivers carry small volumes of water on an irregular basis, and they have seasonally dry river beds; however, when they do flow, they often are swift and torrential. Most major rivers rise in the mountains rimming or dissecting the Meseta Central and flow westward across the plateau through Portugal to empty into the Atlantic Ocean. One significant exception is the Rio Ebro, which flows eastward to the Mediterranean. Rivers in the extreme northwest and in the narrow northern coastal plain drain directly into the Atlantic Ocean. The northwestern coastline is also truncated by rias, waterbodies similar to fjords.

The major rivers flowing westward through the Meseta Central include the Rio Duero, the Tagus, the Rio Guadiana, and the Rio Guadalquivir. The Rio Guadalquivir is one of the most significant rivers in Spain because it irrigates a fertile valley, thus creating a rich agricultural area, and because it is navigable inland, making Seville the only inland river port for ocean-going traffic in Spain. The major river in the northwest region is the Rio Mino.