(IDEX Online) - Twelve people have died and 4,400 have been taken ill after toxic waste from Angola's biggest diamond mine polluted drinking water, say officials in the neighboring Democratic Republic of Congo (DRC).Tailings from the Catoca mine - in which Alrosa (Russia) and Endiama (Angola) both hold 41 per cent stakes - leaked into tributaries of the River Congo, turning the water red and killing fish, as well as two hippopotamuses, and causing an "environmental disaster".The cause of the pollution wasn't immediately clear, but multiple news sources, including Reuters and the BBC, lay the blame squarely with Catoca. The Sociedade Mineira de Catoca (Catoca Mining Company), which operates the mine, has since acknowledged that waste material leaked into the river, filling waterways with sediment before the breach was sealed. The government in DRC warned people not to eat the tons of dead fish floating on the river's surface. Samples revealed there was nickel and iron in the water.Eve Bazaiba, the country's minister of environment, said she would be seeking compensation from the diamond mine owners. "It's a total destruction of ecosystems, especially aquatic biodiversity," she said.Catoca is by far Angola's top diamond producing operation, responsible for approximately three-quarters of the country's output. It also one of the biggest diamond mines in the world.Alrorosa said in a statement: "Alrosa as a responsible minority shareholder of Catoca, an Angolan diamond miner, is committed to bringing more transparency, and has offered its support and expertise to remedy the consequences of the spill."We have also approached Endiama for comment.Pictures, courtesy Congo Basin Water Resources Research Centre, show red river water and dead fish.