LONDON, U.K.: A London court has placed global mining giant BHP Group on the hook for Brazil's deadliest environmental catastrophe, ruling that the company bears legal responsibility for the 2015 dam collapse that sent toxic waste cascading through communities and into one of the country's major rivers.

High Court Justice Finola O'Farrell found that BHP was liable despite not owning the dam outright at the time, concluding that the company's negligence, carelessness, or lack of skill contributed to the failure. BHP holds a 50 percent stake in Samarco, the Brazilian mining company that operated the iron ore facility where the tailings dam gave way on Nov. 5, 2015.

The collapse caused a deluge of mine waste that obliterated the village of Bento Rodrigues in Minas Gerais state and damaged numerous towns downstream. A study by the University of Ulster estimated the volume of sludge as enough to fill 13,000 Olympic-sized swimming pools. The waste polluted 600 kilometers (370 miles) of the Doce River and killed 14 tons of freshwater fish. Nearly a decade later, the river, revered by the Krenak Indigenous people as a deity, remains contaminated with heavy metals.

Legal battles have dragged on since the disaster, delaying reconstruction and reparations. The ruling comes as Brazil positions itself as an environmental leader while preparing to host the U.N. COP30 climate summit, a contrast that advocates say highlights regulatory failures that enabled the disaster.

"We had to cross the Atlantic Ocean and go to England to finally see a mining company held to account," said Mônica dos Santos of the Commission for Those Affected by the Fundão Dam.

The families of the victims also welcomed the judgment. Gelvana Rodrigues, whose seven-year-old son Thiago was killed in the mudslide, said she would continue pursuing accountability. "The judge's decision shows what we have been saying for the last 10 years: it was not an accident, and BHP must take responsibility for its actions," she said.

In the 222-page decision, O'Farrell agreed with lawyers representing 600,000 Brazilians and 31 communities who argued that BHP was deeply involved in Samarco's operations and encouraged raising the dam to increase production. "The risk of collapse of the dam was foreseeable," she wrote. "It is inconceivable that a decision would have been taken to continue raising the height of the dam in those circumstances, and the collapse could have been averted."

BHP said it plans to appeal the ruling.

The class-action suit seeks £36 billion (US$47 billion) in compensation. The judgment addressed only liability; a second phase of the trial will determine damages. The case was brought in the U.K. because one of BHP's two main legal entities was based in London at the time.

The trial began in October 2024, shortly before Brazil's federal government reached a multibillion-dollar settlement with the mining companies. Under that deal, Samarco — co-owned by Vale — agreed to pay 132 billion reais ($23 billion) over 20 years to compensate for human, environmental, and infrastructure damage.

BHP had argued that the U.K. case duplicated the Brazilian settlement. The judge ruled that claimants who received compensation in Brazil could still pursue claims in London, though some may be limited by waivers they previously signed. Brandon Craig, BHP's president of Minerals Americas, said nearly half of the claimants could be removed from the case for that reason.

BHP shares dropped more than two percent in London following the ruling, and the company said it would update its financial provisions.