Ebro River, the longest in Spain. The Ebro rises in springs at Fontibre near Reinosa in the Cantabrian Mountains, in the Cantabria province of northern Spain. It flows for 565 miles (910 km) in a southeasterly course to its delta on the Mediterranean coast in Tarragona province, midway between Barcelona and Valencia. The Ebro has the greatest discharge of any Spanish river, and its drainage basin, at 33,000 square miles (85,500 square km), is the largest in Spain; the river drains about one-sixth of the country. Because it plunges through the coastal mountain ranges by a series of deep gorges and defiles, the Ebro is navigable upstream for only 15 miles (25 km), from its delta to the city of Tortosa.