The Fly River System
The Ok Tedi copper mine is situated in the headwaters of the Ok Tedi, which is a tributary of the Fly River. 'Ok' means 'river' in the local language. The Strickland River is also a tributary to the Fly, but is not affected by OTML's mining operations.
The Fly River is the twenty-third largest river system in the world. It has a total catchment area of about 76,000 square kilometres. It generally discharges between 3,000 and 7,000 cubic metres of water per second to the Gulf of Papua. This was reduced to around 1,000 cubic metres per second during the 1997 El Nino drought.
The river system, with its huge estuary and massive flood plains, lakes and tributaries, supports one of the richest fish, aquatic and wetland fauna in the Australasia and Indowest Pacific region. It is home to approximately 120 fish species as well as turtles, crocodiles and many other amphibians and reptiles.
Local and commercial fishing activities in the Fly River have increased significantly in 
recent years and are an important source of food and revenue for communities. Barramundi and fresh water prawns are fished commercially. Catfish and shellfish are important subsistence food sources for local communities.
The middle and lower reaches of the Fly River are characterised by a wide meandering stream with an extensive forested and grassed flood plain and numerous off-river water bodies and swamps. This flood plain, which extends over about 1,000 square kilometres of the river system, is typically wet or flooded for most of the year.
The very high rainfall in the headwaters and tendency towards frequent landslips causes large amounts of natural sediment to wash into the river system. The Fly River carries a natural sediment load of about 10 million tonnes each year.
An average of 90 million tonnes per year of tailings, overburden and mine-induced erosion are discharged to the Ok Tedi each year from the Ok Tedi mine. About 50 million tonnes of this reaches the Fly River. This additional sediment load has significant impacts on the river system that are discussed in the Impacts of Mining and Managing Mine Waste sections.
Downstream of its confluence with the Strickland River, the Fly River carries 90 million tonnes per year of sediment, of which 70 million tonnes is derived from the Strickland itself. This reflects the Strickland's high natural silt load.