As the longest river in Spain, the Ebro rises in the Cantabrian Mountains of Northern Spain, and parallels the French border on the east. With a course of 575 miles, the river's "headwaters lie in the province of Santander only 40 miles from the Bay of Biscay, the Ebro River follows a southeasterly course through Zaragoza out into the Mediterranean Sea, south of Barcelona. This river has the greatest discharge of any Spanish River with the largest drainage basin of 33,000 square miles. A strategic location, the Ebro River has been a battle site fought between Moors and Christians during the Middle Ages and again during the Spanish Civil War among other clashes.
As the deepest and most navigable, the Guadalquivir River courses approximately 400 miles, making it one of the country's most significant waterways. It begins in the southern Jaén province and flows in a westward direction to the north of the Sierra Nevada Mountain range which fronts the Mediterranean Sea. The river courses northward through a narrow valley, and then moves southwestward passing Córdoba before it reaches Sevilla into the Gulf of Cádiz near Sanlúcar de Barrameda. There, it empties into the North Atlantic Ocean. Salty marshlands line the southern portion of the river as it makes its way to the sea. Navigable by land, the Guadalquivir River makes Seville a major inland river port for ocean-going vessels in Spain.
On the slopes of Teruel, in the Aragón region, starts the longest waterway on the Iberian Peninsula, the Tagus (Tajo) River. It rises in the Sierra de Albarracin of eastern Spain within proximity to the Mediterranean coastline. From there, it flows westward until it empties into the North Atlantic Ocean closer to Lisbon with a distance of 625 miles. The Tagus River traverses deep gorges, broken up by surging cascades on its lower and upper courses. According to United Nations Environmental Program, "part of the flow in Spain is diverted to the Segura basin, supplying 1.5 million people in southern Spain with drinking water, providing irrigation and supporting the ecosystem in the La Mancha Nature Reserve."
