The Wadden Sea is a UNESCO World Heritage Site that consists of the southeastern part of the North Sea. It lies between the Netherlands, Germany and Denmark. The sea has a surface area of around 10,000 km2 and consists mostly of tidal mud flats. The sea is famous for its rich nature, especially its birds. The sea is home to hundreds of thousands of ducks, geese and other migratory birds. The sea is furthermore an important habitat for seals and dolphins. The islands of the Wadden Sea are popular seaside resorts, with mudflat hiking being a popular tourist activity.