BHP Billiton mining company is being sued in the UK for 4 billion pounds, Financial Times reports. The company is accused of ignoring warning signals for a breakthrough of a dam around a wastewater reservoir at a Brazilian mine in 2015. This breakthrough led to the largest environmental disaster ever in Brazil.

The case was brought on behalf of 235,000 people and companies. BHP Billiton says in a response that it wants to defend itself against the damage claim.

The breakthrough released 55 billion liters of waste water, which led to a mudflow that killed at least seventeen people. The breakthrough took place at an iron mine owned by BHP Billiton and Vale. Three months ago, at a mine at the latter company, a dyke breach occurred in which more than three hundred people died.