The Wadden Sea is an intertidal zone of the North Sea [the word ‘wad’ is Dutch for ‘mud flat’]. It lies between the coast of northwestern continental Europe and the Frisian Islands [Vlieland is one of them], forming a shallow body of water with tidal flats and wetlands. Here, a multitude of transitional habitats exist with tidal channels, sandy shoals, sea-grass meadows, mussel beds, sandbars, mudflats, salt marshes, estuaries, beaches, and dunes.
The Wadden Sea is home to numerous, highly specialized plant and animal species, including marine mammals such as the harbor seal, grey seal, and harbor porpoise. It is also a breeding and wintering area for up to 12 million birds per annum.