The Parnaíba River (Portuguese: Rio Parnaíba) 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 344,112 km² (132,862 sq mi). 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.