Holidaymakers splash in the turquoise waters of the Rosignano Solvay beach in Tuscany and laze on its pristine white sands -- most of them fully aware that the picture-perfect swimming spot owes its allure to a nearby factory. "I discovered it on Google Maps," said Dutch tourist Lieuya, who travelled to the beach with his family to enjoy a setting more reminiscent of the Caribbean than of northern Italy.

"I was told it's not dangerous, that the colour comes from the soda factory next door," he told AFP. Questions have lingered for decades over why the sea and sand are such startling colours -- with some environmentalists suggesting the phenomenon is caused by heavy metals emitted by the plant.