The Iguazu River is a river in Brazil and Argentina. It is an important tributary of the Parana River. The Iguazu River is 1,320 kilometres (820 mi) long, with a drainage basin of 62,000 square kilometres (24,000 sq mi). The Iguazu originates in the Serra do Mar coastal mountains of the Brazilian state of Paraná. For 1,205 kilometres (749 mi), to its confluence with the San Antonio River, the Iguazu flows west through Paraná State, Brazil.
Downriver from the confluence the Iguazu River forms the boundary between Brazil and Argentina's Misiones Province. Continuing west, the river drops off a plateau, forming Iguazu Falls. The falls are within national parks in both Brazil, Iguaçu National Park, and Argentina, Iguazú National Park. It empties into the Paraná River at the point where the borders of Argentina, Brazil, and Paraguay join, and area known as the Triple Frontier.