The Guadalquivir, stretching over 657 km, is the fifth longest river in the Iberian Peninsula, and it is also the only navigable river in Spain. Situated in Andalusia, the open part goes from Cadiz to Sevilla. This navigable part also includes the Doñana National Park. The Guadalquivir is also hosting a species of fish unique in the world. The particularity of this fish is that he doesn't have the right number of chromosomes.