The Spanish landscape is rich with rivers, and these waterways are useful in the generation of hydroelectric power, irrigating fields and vineyards, preserving the local environment, and providing scenic views. The major rivers of the country include the Tagus, Ebro, Douro, Guadiana, Jucar, and more.

The longest river in Spain is the Ebro, also known as Iberus or Hiberus, which runs for over 578 miles from its source in the Cantabrian Mountains to its delta on the Mediterranean Sea. The Ebro has over 200 tributaries, and its drainage basin is the largest in the country.

Another significant river is the Guadiana, which flows through northern Spain and Portugal. It defines part of the border between the two countries, and stretches over 355 miles. The Douro, the fourth largest river in the country, is a long, meandering river that forms wide river valleys among limestone rocks. Its tributaries include the Valdevila, Moreira, and Genil, and it defines part of the border between Portugal and Spain.

The Tagus, which drains the capital of Madrid and flows to Lisbon in Portugal, is a vital resource for the six million people who live in the city. The river is used to supply the metro, cool nuclear reactors, and for other purposes. However, its future is uncertain due to climate change and water transfers. Nuria Hernandez-Mora, an environmental lawyer, said that the problem is exacerbated by the fact that Spain doesn't have enough wetlands to absorb excess rainfall.