The original environmental impact statement for the mine had required a proper tailings dam. It was meant to catch the heavy metals and solid particles, let the toxic sludge settle, and release only the less-contaminated upper water into the river system, where remaining pollutants could be diluted by a river known for huge discharge. The Ok Tedi is, after all, the principal tributary of the Fly River — one of the world's largest rivers by volume and the largest in the world without a single dam in its catchment. The seismic activity that plagues the Star Mountains collapsed the half-completed structure before it could be finished. BHP, then majority owner, argued against rebuilding it. The government concurred. So began what is known in mining circles as riverine disposal: waste rock, ore processing residues, and overburden sent straight into the Ok Tedi with no retention facilities whatsoever.

The scale of the damage is difficult to hold in mind. By 1999, BHP's own reporting acknowledged that 90 million tons of mine waste were being dumped into the river each year, that waste had been deposited along 1,000 kilometers of river, and that destruction covered 100 square kilometers of countryside. About 1,588 square kilometers of forest has died or is under stress; eventual harm may reach 3,000 square kilometers, an area the size of the U.S. state of Rhode Island or the Danish island of Funen. The riverbed itself rose by ten meters. A relatively deep, slow river became shallow and broken by rapids, disrupting the canoe routes that villages had used for generations. Flooding caused by the raised bed laid a thick gray sludge over 1,300 square kilometers of floodplain — directly onto plantations of taro, bananas, and sago palm that are staples of the local diet.

The Yonggom people of the lower Fly region and their neighbors — around 50,000 people in 120 villages — were the ones who had to live with it. Fish stocks collapsed near the mine. Copper concentrations in the water ran roughly thirty times above standard levels, though still below World Health Organization drinking-water thresholds. Fish that remained were often contaminated, and still eaten, because there was little other choice. In the 1990s, communities sued BHP. An out-of-court settlement in 1996 produced US$28.6 million along with a modest dredging operation and some rehabilitation efforts near the mine site. As part of the settlement BHP received legal indemnity from future claims. BHP's own CEO, Paul Anderson, said publicly in 1999 that the Ok Tedi Mine "is not compatible with our environmental values and the company should never have become involved." The waste kept flowing.

In 2002 BHP Billiton transferred its majority shareholding to the PNG Sustainable Development Program. In 2013, the government of Papua New Guinea seized 100% ownership of the mine and passed legislation specifically repealing laws that would have allowed affected communities to sue BHP over future damage. BHP responded calmly, noting that it had other legal indemnities in place to protect shareholders from further liability. The mine itself, originally scheduled to close in 2013, had its life extended after 156 villages in the Mine Associated Communities signed new continuation agreements at the end of 2012 and early 2013. Two-thirds of profits are now directed into a long-term fund meant to keep contributing to the PNG economy for up to 50 years after closure. One-third funds local and national development programs.

From space, the damage is legible. The Ok Tedi River reads as a pale gray scar threading south from the mountains. The forest along the floodplain is mottled with dead patches. The Fly River, downstream of the confluence, turns thick and slow with sediment that settles across broad shallows. The downstream effects are also subtler — areas of deep spiritual value to local villages, places named in songs and stories, are now submerged under tailings. The United Nations Environment Programme has described the pollution as having caused "flooding, sediment deposition, forest damage, and a serious decline in the area's biodiversity." What the satellites cannot show is the daily negotiation of life along a ruined river — the families still catching and eating fish because there is nothing else, the generations that now associate their ancestral country with loss.