Paraná, river, c.2,000 mi (3,200 km) long, formed by the junction of the Paranaíba and the Rio Grande, SE Brazil. It has the second largest drainage system in South America. It flows generally southwest to its confluence with the Paraguay River, forming the southern border of Paraguay, then S and E through NE Argentina to join the Uruguay River in a huge delta at the head of the Río de la Plata. The lower Paraná is hampered by shifting channels, sandbars, and fluctuating river flow, and is subject to flooding. The stretch along the Brazil-Paraguay border flows in a deep bed and is broken by many waterfalls, now submerged under the large Itaipú Dam, built in the late 20th cent. Downstream at Encarnación, Paraguay, the river is crossed by the Yacyretá dam. The Paraná is the principal commercial artery of interior SE South America. Navigable for oceangoing vessels (via a dredged channel) to Rosario and Santa Fe in Argentina, the Paraná accommodates river craft to the Iguaçu River. A bridge over the river at Foz do Iguaçu links Brazil and Paraguay. The Paraná was first ascended (1526) by Sebastian Cabot, the English explorer in the service of Spain.