The Wad­den Sea is the largest unbro­ken sys­tem of inter­tidal sand and mud flats in the world. The site cov­ers the Dutch Wad­den Sea Con­ser­va­tion Area, the Ger­man Wad­den Sea Nation­al Parks of Low­er Sax­ony and Schleswig-Hol­stein, and most of the Dan­ish Wad­den Sea mar­itime con­ser­va­tion area. It is a large, tem­per­ate, rel­a­tive­ly flat coastal wet­land envi­ron­ment, formed by the intri­cate inter­ac­tions between phys­i­cal and bio­log­i­cal fac­tors that have giv­en rise to a mul­ti­tude of tran­si­tion­al habi­tats with tidal chan­nels, sandy shoals, sea-grass mead­ows, mus­sel beds, sand­bars, mud­flats, salt marsh­es, estu­ar­ies, beach­es and dunes. The area is home to numer­ous plant and ani­mal species, includ­ing marine mam­mals such as the har­bour seal, grey seal and har­bour por­poise. Wad­den Sea is one of the last remain­ing large-scale, inter­tidal ecosys­tems where nat­ur­al process­es con­tin­ue to func­tion large­ly undis­turbed.