The Zwin is a former sound that is now silted up and lies between the resort and Dutch border. It once served the ports of Sluis, Damme et Bruges. It is now a nature reserve, with a section open to the public, and is home to interesting flora and fauna. It is a world of tide-related channels and salt meadows surrounded by dunes and dikes. It is full of birds in the spring, including terns or avocets and offers a mauve carpet of flowers in summer.