The Ok Tedi environmental disaster caused severe harm to the environment along 1,000 km (620 mi) of the Ok Tedi River and the Fly River in the Western Province of Papua New Guinea from 1984 to 2013, with the damage still ongoing. The lives of 50,000 people have been disrupted by the disaster. One of the worst environmental disasters caused by humans, it is a consequence of the discharge of about two billion tons of untreated mining waste into the Ok Tedi from the Ok Tedi Mine, an open pit mine situated in the province.
This mining pollution, caused by the collapse of the Ok Tedi tailings dam system in 1984 and the consequent switch to riverine disposal (disposal of tailings directly into the river) for several decades, was the subject of class action litigation brought by local landowners naming Ok Tedi Mining and BHP Billiton. Villagers downstream from Ok Tedi in the Fly River system in the Middle Fly District and the southern and central areas of the North Fly District in particular believe that the effect on their livelihood from this disaster far outweighs the benefits they have received from the mine's presence in their area.