The Fly River is the second longest river in Papua New Guinea, after the Sepik. The Fly is the largest river in Oceania, the largest in the world without a single dam in its catchment, and overall ranks as the 25th largest river in the world by volume of discharge. It rises in the Victor Emanuel Range of the Star Mountains, and crosses the south-western lowlands before flowing into the Gulf of Papua.
The Fly flows mostly through the Western Province, though for a small stretch it forms the boundary between PNG and the Indonesian Province of Papua. To compensate for this slight gain in territory for PNG, the border south of the Fly River is slightly east of the 141 E longitude line. As part of this deal, Indonesia has the right to use the Fly River to its mouth for navigation.
The tributaries of the Fly are the Strickland and Ok Tedi.
Close to its mouth, the flow of the Fly River encounters a tidal bore, where an incoming high tide pushes water upstream until the changing of the tide, the range of this tidal bore is still not documented.
Length: 1,050 km
Discharge: 6,000 m3/s
Basin area: 76,000 km2
Mouth: Gulf of Papua New Guinea