Largest contiguous intertidal mudflats

Stretching 450 kilometres (280 miles) along the northern European coastline from the Netherlands to Denmark lies the Wadden Sea. Its shallowness gives it a rich diversity of habitats including tidal channels, sea grass meadows, sandbars, mussel beds and salt marshes. It is classified as a UNESCO World Heritage site, and encompasses the area between the shore and the Friesian Islands archipelago, with a total area of around 11,400 square kilometres (4,400 square miles). The area is a key region for migratory birds, with 10–12 million passing through each year and up to 6.1 million present at any one time.