The Ebro and Douro are two rivers that flow through Spain and Portugal. The Ebro is the longest river in Spain, stretching for 910 kilometers from its source in the Cantabrian Mountains to its mouth on the Mediterranean Sea. The Douro is a river in northern Portugal, flowing for 897 kilometers from its source in the Serra da Estrela mountains to its mouth on the Atlantic Ocean. Both rivers are important sources of water for the countries they flow through, providing irrigation and hydroelectric power.