The Douro River is one of the major waterways on the Iberian Peninsula; it's the third-longest after the Ebro and the Tagus. The Douro rises in northern Spain and runs a course of just under 900 km (around 550 mi.), emptying into the Atlantic in the Portuguese city of Porto. For about a fifth of its run it forms the national boundary between Portugal and Spain. With 15 dams, it's also a significant source of hydropower. In this drone video, you'll see a stretch of the river as it runs through Portugal's wine country.