The Fly River and its tributaries head in the fold and thrust belt of New Guinea where nearby peaks reach up to 4000m. The river has three primary branches, the Ok Tedi , the Fly and the Strickland. The Ok Tedi joins the Fly at about 18 m above mean sea level where the river is 846 km from the delta mouth.
Small landslides are common, and large ones can be spectacular.
Reworking and dispersal of landslide introduced sediment downstream is rapid. The floodplain system is composed of an inner scoll bar complex bordered by backswamp and blocked valley swamps. Dietrich et al. By 1992 the total input of sediment associated with the mine activity was 501 million tonnes. This is will be nearly 14 times the natural load on the Ok Tedi.