Paraná River, 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, southeastern Bolivia, and northern Argentina. From its origin at the confluence of the Grande and Paranaíba rivers to its junction with the Paraguay River, the river is known as the Alto (Upper) Paraná. This upper course has three important tributaries, namely the Tietê, the Paranapanema, and the Iguaçu, all three having their sources near the Atlantic coast in southeastern Brazil. The Alto Paraná’s passage through the mountains was formerly marked by the Guaíra Falls; this series of massive waterfalls was completely submerged in the early 1980s by the reservoir of the newly built Itaipú dam complex, which spans the Alto Paraná.

From its confluence with the Iguaçu River to its junction with the Paraguay River, the Alto Paraná continues as the frontier between Paraguay and Argentina. When it is joined by the Paraguay, it becomes the lower Paraná and commences to flow only through Argentine territory. Near Santa Fé, the lower Paraná receives its last considerable tributary, the Salado River. Between Santa Fé and Rosario the delta of the Paraná begins to form, being 11 miles (18 km) wide at its upper end and roughly 40 miles (65 km) wide at its lower end. Within the delta the river divides again and again into distributary branches, the most important being the last two channels formed, the Paraná Guazú and the Paraná de las Palmas.

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The volume of the lower Paraná River is dependent on the amount of water that it receives from the Paraguay River, which provides about 25 percent of the total; the Paraná’s annual average discharge is 610,700 cubic feet per second (17,293 cubic metres per second). The basin of the Alto Paraná has a hot and humid climate year round, with dry winters and rainy summers. The climate of the middle and lower basins ranges from subtropical in the north to temperate humid in the south, with less plentiful rainfall. The Alto Paraná has two zones of vegetation, forests to the east and savanna to the west. Forests continue along the Paraná downstream to Corrientes, where the savanna begins to dominate both banks. The Paraná River has a rich and varied animal life that includes many species of edible fish. Much of the Paraná basin is economically unexploited. The main dam of the huge Itaipú project on the Paraná River was completed in 1982 and had a power generating capacity of 12,600 megawatts. The Yacyretá Dam on the lower Paraná River began operation in 1994. The lower river is a transport route for agricultural products, manufactured goods, and petroleum products, and its waters are used for irrigation of the adjacent farmlands.