It was Somerset Maugham who said the French Riviera is “a sunny place for shady people” – and looking around at all the 'models' in the hotel lobbies and the men in dark sunglasses who seemed to know them, I knew what he meant. Behind the festival's shiny facade, there is an unseemly side – and beneath the azure waters, a polluted mess. The French diver and environmentalist Laurent Lombard's video of the Cannes seabed strewn with waste and debris went viral before the festival began. We were assured there was no danger to swimmers, and the mayor had it cleaned up according to the Daily Mail – but the Med had certainly lost some of its sparkle.