The Doñana Disaster, also known as the Aznalcollar Disaster or Guadiamar Disaster, was an industrial accident in Andalusia, southern Spain. On 25 April 1998, a holding dam burst at the Los Frailes mine, near Aznalcóllar, Seville, releasing 4–5 million cubic metres (3,200–4,100 acre⋅ft) of mine tailings. The acidic tailings, which contained dangerous levels of several heavy metals, quickly reached the nearby River Agrio, and then its parent river, the River Guadiamar, travelling about 40 kilometres (25 mi) along these waterways and covering an area of 4,600 hectares before they could be stopped. The Guadiamar is the main water source for the Doñana National Park, a UNESCO World Heritage Site and one of the largest national parks in Europe. The cleanup operation took three years, at an estimated cost of €240 million.