There are over 1,100 tributaries that flow into the Amazon River. The three longest are the Madeira River(1), Purus River(2) and the Japur River(3).Madeira River
The main rivers in Spain are the Duero (Douro), Miño, Tajo (Tagus), Guadiana , the Guadalquivir River, and the Ebro River. These rivers are an awesome source of electric power. Hope this helps :)