The view from the visitors’ centre at the southern edge of Doñana National Park in southern Spain is striking, to say the least. This is an ornithologist’s dream: 200,000 hectares of salt marsh of unrivalled importance to the birdlife of western Europe. Dozens of Britain’s most loved migratory birds, including house martins, swallows, cuckoos and warblers, rest here on their annual migrations from Africa. Doñana, a UN World Heritage Site, is also home to some of Europe’s rarest birds, including the Spanish imperial eagle, while its mammalian inhabitants include the highly endangered Iberian lynx. It is a glorious, vibrant landscape. Yet it exists on a knife-edge, a point illustrated dramatically in 1998 when almost two billion gallons of contaminated, highly acidic water, mixed with waste metals, poured into the park from a dam that had burst its bank at Los Frailes mine 45km to the north. A toxic tsunami of waste poured down the Guadiamar river and over its banks, leaving a thick metallic crust over a vast stretch of parkland. More than 25,000 kilos of dead fish were collected in the aftermath and nearly 2,000 adult birds, chicks, eggs and nests were killed or destroyed. It was Spain’s worst environmental disaster and the clean-up cost €90m. Suddenly aware of Doñana’s status as the nation’s most important natural site, Spain decided to spend a further