The morning is cold and damp and the mist has barely risen from the Doñana marshes. But, at Vicente Gonzalez's strawberry farm in a pine forest bordering Europe's most important protected wetlands, they've been picking strawberries since daybreak. In the coming days Mr Gonzalez will take on another 25 pickers, from Romania, Poland or Morocco, who will work until June, after which the fruit turns to mush and the price plummets.
"I rent this land from the local council and they grant me permission to use three wells to irrigate my strawberries," Mr Gonzalez, 37, says as he watches workers bring piles of plywood boxes each laden with 2kg of fruit and pass them up to José who stows them in the company lorry.
"Those are going to England," says Mr Gonzalez´s wife, Francisca, pointing to wide black plastic trays where the boxes are laid. When the day's crop is loaded, the lorry will head for the producer's co-operative at Lucena del Puerto and the trays of strawberries will be driven to Britain. Within two days of being picked, they'll be in a supermarket near you.
Vicente and Francisca Gonzalez say all their permits are in order. But Mr Gonzalez's farm - like half those in the Huelva region, which supplies almost all Britain's winter strawberries - is illegal. It occupies public forest that has never been classified for agriculture. And the water that the council allows Mr Gonzalez to draw is not theirs to give, but the responsibility of the regional water authority.
From the lane that winds through woodland and rosemary, thyme and pistachio bushes, you can glimpse dozens of plots gouged from the forest, covered in tunnels of plastic. The use of hundreds of illegal wells to irrigate strawberries has caused the underground water level in this fragile ecosystem to drop by 50 per cent in recent years, a dramatic fall that threatens irreversible damage to the protected wetlands.
Strawberry production started in Huelva province 20 years ago, supplying Spain, and now Germany, Holland and Britain, with winter fruit. The area is not called the Costa de la Luz (Coast of Light) for nothing. Long hours of sunshine and mild sea breezes make it ideal for growing. But all that comes at a heavy environmental cost only now becoming evident.
Deep in the forest, Javier Serrano, water commissioner for the Guadalquivir river basin authority, drops a stone and counts to three before we hear a splash. This illegal well is about 30 metres deep. Nearby is an electricity cable, tapped illegally from some strawberry farm, to power the pump. It's one of 1,300 illegal boreholes sunk to the underground source of the Rocina river.
Mr Serrano, who is employed by the Environment Ministry in Madrid, was appointed two years ago by the socialist government to monitor and shut down illegal wells in the Guadalquivir river basin, most of which are around the Doñana.
He has closed 220, mostly only provisionally. "It's far too few. The task outstrips the resources we have," he says. "It's a big social problem because the small villages depend on strawberry farming for their livelihood, and the mayors defend the farmers. People were not aware of the environmental consequences."
Creeks such as the Peral that feed into the Rocina and the Doñana have dwindled to a trickle, strangled by filthy sheets of discarded plastic. These streams used to support a rich diversity of riverbank vegetation and fauna, providing migration routes and drinking water for endangered animals now on the brink of extinction: the Iberian Lynx, the otter, the Egyptian mongoose and the genet. Deprived of natural corridors that criss-cross their habitat, the bewildered creatures dash into the road and are run over- the main cause of death.
The Rocina creek, in a protected area bordering the Unesco Natural World Heritage site of the Doñana National Park, dribbles into the precious marshlands. "Our old people always used to say that of all the arroyos - rivers that dry up in April or May - the Rocina was the only one that kept a constant flow of running water," says Felipe Fuentelsaz, the Worldwide Fund for Nature's Doñana agriculture officer, who grew up in this area. Even in burning August, small springs supplied water for lagoons where flamingos, storks and herons gathered to feed and preen. But in the past three years, the Rocina has been parched from July to October.
Eventually, the deep lagoons will evaporate, the sandy dunes will erode; Europe's most important wetlands will be transformed into dry savannah grasslands, and hundreds of thousands of water fowl will be forced to go elsewhere, Mr Fuentelsaz says.
"We can't ask northern European consumers to boycott strawberries," says Guido Schmidt, head of WWF Spain's freshwater programme. "It's not realistic and would hurt the livelihoods of thousands of farmers. We prefer to encourage best practice and urge supermarkets to ensure they buy only from legal farms."
That is a big enough challenge but one big supermarket chain in The Netherlands is already co-operating, and promises to attach to each punnet of strawberries a little leaflet about protecting the Doñana. "We plan to write to the main British supermarkets urging them to ensure, over coming years, that their strawberries come from legal farms," Mr Schmidt says. But illegal and legal farmers alike complain the demanding English market is pushing them to their limits. "They make our life very difficult," they say.
WWF is campaigning for the recovery of degraded creeks, and wants to clean them up and transform them into "ecological corridors" to support the diversity of wildlife essential to the ecosystem.
Mr Schmidt believes that farmers on illegally cleared land could be offered subsidies to relocate. Producers in Huelva know that their region is almost completely saturated. If ground water continues to be depleted, their own irrigation water will become scarcer, saltier, and more concentrated with minerals and chemical residues from fertilizer.
But, by then, the unique natural paradise of the Doñana wetlands, meeting point of the Guadalquivir river and the Atlantic Ocean, intercontinental crossroads for migrating birds, will have entered an irreversible decline.