The delta of the Fly River is over 100 km wide at its entrance, but only 11 km wide at the apex upstream of Kiwai Island. The delta contains 3 main distributary channels (the Southern, Northern, and Far Northern Entrances) that branch from a common point (the “apex”). The distributary channels are 5 to 15m in depth, separated by elongate, sand-mud islands that are stabilised by lush mangrove vegetation. The islands are eroded and rebuilt rapidly in the apex area, where they have lateral migration rates of up to 150 m/a, with slower rates for the more seaward islands. Upstream from the apex the river gradually narrows to a width of 1.6 km or less. The Fly Delta exhibits a distinctive funnel shape in plan view, attesting to the fundamental role of tidal currents in shaping the Delta's geomorphology. Mean spring tidal ranges are amplified within the delta, from around 3.5m at the seaward entrance of the distributary channels, reaching a peak of about 5m at the delta apex. Seismic profiles and radiometrically dated core samples indicate that the delta is prograding seawards at an average rate of about 6 m/a