A High Court judge in the United Kingdom has ruled that mining giant BHP Group is legally responsible for the 2015 collapse of a tailings dam in Brazil, the country’s most serious environmental disaster.

Justice Finola O’Farrell said on November 14 that BHP bore liability under Brazilian law even though the company did not directly own the dam at the time of the incident.

In November 2015, a tailings structure at the Samarco iron ore operation failed, releasing waste that coursed through the Rio Doce basin. Nineteen people died, villages were heavily damaged and thousands were forced to leave their homes. 

BHP holds a 50% stake in Samarco, alongside Vale. Researchers from the University of Ulster have estimated that mine waste spread across 600 kilometres of the river system and caused the death of 14 tonnes of freshwater fish, AP reported.

O’Farrell said the decision to keep increasing the height of the dam despite known risks was the “direct and immediate cause” of the collapse. She found that BHP was sufficiently involved in Samarco’s activities to have prevented the failure. 

Class-action lawyers representing 600,000 Brazilians and 31 communities argued BHP supported the dam-raising strategy to enable higher 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, now headquartered in Australia, said it would appeal the judgment. Brandon Craig, President Minerals Americas, said in a statement that many of the 240,000 people included in the London claim “have already been paid compensation in Brazil”.

The lawsuit was brought in the UK because one of BHP’s principal corporate entities was registered in London at the time. The trial opened in late 2024, shortly before Brazil’s federal government reached a separate agreement with Samarco and Vale. The ruling reportedly covered only the legal liability for the disaster, with a second phase of the trial expected to determine damages.

That deal requires BRL132bn ($24.8bn) in payments over 20 years for social, environmental and infrastructure damage.

“We had to cross the Atlantic Ocean and go to England to finally see a mining company held to account”, Mónica dos Santos, from the Commission for Those Affected by the Fundão Dam, told AP.

“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,” said Gelvana Rodrigues, whose son died in a mudslide.