The Landscape
The main island of New Guinea is the second largest in the world after Greenland. It was formed over thousands of millennia as the Pacific and Indo-Australian tectonic plates collided. The main island is shared by two countries: Papua New Guinea and West Papua, the 26th province of the Republic of Indonesia.
The Western Province of PNG lies between five and ten degrees latitude. It is bounded by West Papua to the west, PNG's Sandaun Province to the north, and Australia, four kilometres off the coast to the south.
It has extremely high rainfall up to 11 metres in the central ranges and highly leached, infertile soils.
The environment of the Western Province very much dictates how and where people live, with a large proportion of the population traditionally living in the lowlands and along the major river systems where soils are more fertile and rainfall less intense.
The Western Province is large, sparsely populated and isolated. It has an area of 97,000 km2, one fifth of the area of Papua New Guinea. Vegetation varies across the province with changes in topography, rainfall and temperature.
On brackish mudflats and low-lying islands of the massive Fly River estuary which covers approximately 7,000 square kilometres vegetation is predominately mangrove forest. Tropical lowland rainforest, open savannah grassland, swamp plants and large sago stands are found above the limits of the tide. These extend up river to around Suki in the lower Fly. Fires are a frequent feature of the savannah grasslands during the dry season.
Above Suki and Sturt island as far as Obo and the junction with the Strickland River, the vegetation is largely grassed floodplain, with predominately aquatic and semi-aquatic species. In the middle Fly, 
beyond Obo up to D'Albertis Junction at the base of the Ok Tedi, vegetation is mainly lowland rainforest mixed with swamp forest. Rainforest predominates above D'Albertis Junction.
There is an abrupt increase in altitude and increasingly rough terrain between Ningerum on the Ok Tedi and Tabubil at about 600 metres above sea level. Vegetation is high in diversity and comprises a mixture of lowland and lower montane rainforest species. Above about 1,000 metres, the vegetation is predominately montane rainforest. These are moist forests with many mosses and ferns. They are notable for their diversity of mammals, which is the highest recorded in PNG.
Due to its position at the intersection of two tectonic plates, the northern part of the Western Province is characterised by unstable, steep upthrust mountains where landslips are common. The high rainfall and unstable mountain terrain result in high levels of erosion and, consequently, many rivers such as the Strickland carry very high natural silt loads.
The Ok Tedi mine is situated in rugged mountain terrain on Mount Fubilan in the southern slopes of the Star Mountains, about 15 km from the border with West Papua.
The Star Mountains contain the headwaters of the Fly River system. It is a difficult place to operate a mine, and poses special challenges in how best to manage the impacts of mining including disposing of waste rock and tailings from the operations.
In some places, mining has caused significant changes to the landscape, the most obvious of these being silting of the Ok Tedi and Fly River and associated areas of forest dieback. These are discussed in the impacts of mining section.