From sewage and scum to swimming in ‘blue gold’: how Switzerland transformed its rivers

In the 1960s, the Swiss had some of the dirtiest water in Europe. Now, their cities boast pristine rivers and lakes - and other countries are looking to follow their lead

In the first days of spring, people flock to Lake Geneva's broad, tree-lined promenade, their faces tilted towards the sun. Dior, Cartier and Rolex are among the high-end shopfronts overlooking the water. Rene Rottenberg, 75, has just finished his 400m swim through this upmarket urban jungle - a ritual he repeats up to five times a week, even in midwinter.

For the retired gynaecologist, being able to swim in the crystal-clear water is the greatest luxury. It's just so fun," he says. The place is beautiful."