A river of South America, the second longest after the Amazon, rising on the plateau of southeast-central Brazil and flowing generally south to the point where, after a course of 3,032 miles (4,880 km), it joins the Uruguay River to form the extensive Río de la Plata estuary of the Atlantic Ocean. See also Plata, Río de la. The Paraná River's drainage basin, with an area of about 1,081,000 square miles (2,800,000 square km), includes the greater part of southeastern Brazil, Paraguay.