The Parnaíba River (Portuguese: Rio Parnaíba [paɾnaˈibɐ]) is a river in Brazil, which forms the border between the states of Maranhão and Piauí. Its main course is 1,400 km (870 mi) long and the Parnaíba River Basin covers 330,000 km2 (130,000 mi2). The Parnaíba River rises in the Chapada das Mangabeiras range, and flows northeastward to empty into the Atlantic Ocean, being the longest river entirely located within Brazil's Northeast Region. The middle and upper regions of this river are separated by the Boa Esperança Hydroelectric Power Plant dam, but is otherwise navigable.
