A great river of South America, formed by the confluence of the Rio Grande and the Paranahyba, in SE. Brazil, flows SW. through Brazil and round the SE. border of Paraguay, then receiving the Paraguay River, turns S. through the Argentine, then E. till the junction of the Uruguay forms the estuary of the Plate. The river is broad and rapid, 2000 m. long, more than half of it navigable from the sea; at the confluence of the Yguassu it enters a narrow gorge, and for 100 m. forms one of the most remarkable rapids in the world; the chief towns on its banks are in the Argentine, viz. Corrientes, Santa Fé, and Rosario.