The tailings dam at the Los Frailes gold-copper-lead-zinc mine, located at Aznalcóllar near Seville, failed in April 1998. It released approximately 5.5 million cubic metres of acidic, metal-rich water and approximately 1.3 to 1.9 million cubic metres of toxic tailings into the Agrio, Guadiamar and Los Frailes Rivers (WWF 2002). The contamination affected 62 kilometres…