The Wadden Sea stretches fromDen Helder, in the northwest of theNetherlands, past the great riverestuaries ofGermany to its northern boundary atSkallingen inDenmark along a total coastline of some 500 km (310 mi) and a total area of about 10,000 km2 (3,900 mi2). Within the Netherlands, it is bounded from theIJsselmeer by theAfsluitdijk. Historically, the coastal regions were often subjected to large floods, resulting in thousands of deaths, including theSaint Marcellus' floods of 1219 and 1362,Burchardi flood of 1634 andChristmas Flood of 1717. Some of these also significantly changed the coastline.[3][4] Numerousdikes[5] and severalcauseways have been built,[6] and as a result recent floods have resulted in few or no fatalities (even if some dikes rarely and locally have been overrun in recent history).[3][4] This makes it among the most human-altered habitats on the planet.[7]
The wordwad is Frisian and Dutch for "mud flat" (Low German andGerman:Watt,Danish:Vade). The area is typified by extensive tidalmud flats, deeper tidal trenches (tidal creeks) and the islands that are contained within this, a region continually contested by land and sea.[8]
The landscape has been formed for a great part bystorm tides in the 10th to 14th centuries, overflowing and carrying away formerpeat land behind the coastal dunes.[citation needed] The present islands are a remnant of the former coastal dunes.
Towards the North Sea the islands are marked by dunes and wide sandy beaches, and towards the Wadden Sea a low, tidal coast. The impact of waves and currents carrying awaysediments is slowly changing both land masses and coastlines. For example, the islands ofVlieland andAmeland have moved eastwards through the centuries, having lost land on one side and gained it on the other.[9]
Sea level rise poses a significant threat to areas with low-lying coastal areas with small gradients, such as the tidal flats of the Wadden Sea. However, recent studies indicate that the current sea level rise (3.7 mm/yr)[10] is being exceeded by sediment accretion rates across most of these tidal flats, particularly along the German coastline. While tidal flats in the Dutch Wadden Sea are also accreting, they are doing so at a slower pace.[11]
Larger fish includingrays,Atlantic salmon andbrown trout are still present in several sections of the Wadden Sea, but others likeEuropean sea sturgeon only survive in the region through a reintroduction project. The world's only remaining natural population ofhouting survives in the Danish part of the Wadden Sea and it has been used as a basis for reintroductions further south, but considerabletaxonomic confusion remains over its status (whether it is the same as the houting that once lived further south in the Wadden Sea).[18][19]European oyster once formed large beds in the region and was still present until a few decades ago, when extirpated due to a combination of disease and the continued spread of the invasivePacific oyster, which now forms large beds in the Wadden Sea.[20] Especially the southwestern part of the Wadden Sea has been greatly reduced. Historically, theRhine was by far the most important river flowing into this section, but it has been greatly reduced due to dams. As a result, about 90% of all the species that historically inhabited that part of the Wadden Sea are at risk.[21]
The Wadden Sea is an important habitat for bothharbour andgrey seals.Harbour porpoises andwhite-beaked dolphins are the sea's only residentcetaceans. They were once extinct in the southern part of the sea but have also re-colonized that area again.[22] Many other cetaceans only visit seasonally, or occasionally.[23][24] In early history,North Atlantic right whales andgray whales (now extinct in the North Atlantic)[25] were present in the region, perhaps using the shallow, calm waters for feeding and breeding. It has been theorized that they were hunted to extinction in this region by shore-based whalers in medieval times.[26][27] They are generally considered long-extinct in the region, but in the Netherlands, a possible right whale was observed close to beaches onTexel in theWest Frisian Islands and off Steenbanken,Schouwen-Duiveland in July 2005.[28] Recent increases in the number of North Atlantichumpback whales andminke whales might have resulted in more visits and possible re-colonization by the species to the areas especially aroundMarsdiep.[29][30] Future recovery of once-extinct localbottlenose dolphins is also expected.[22]
Although the Wadden Sea is not yet listed as a transboundary Ramsar site, a great part of the Wadden Sea is protected in cooperation of all three countries. The governments of the Netherlands, Denmark and Germany have been working together since 1978 on the protection and conservation of the Wadden Sea. Co-operation covers management, monitoring and research, as well as political matters. Furthermore, in 1982, a Joint Declaration on the Protection of the Wadden Sea was agreed upon to co-ordinate activities and measures for the protection of the Wadden Sea. In 1997, aTrilateral Wadden Sea Plan was adopted.[32][33][34]
In June 2009, the Wadden Sea (comprising the Dutch Wadden Sea Conservation Area and the German Wadden Sea National Parks of Lower Saxony and Schleswig-Holstein) was placed on theWorld Heritage list byUNESCO.[36] A minor boundary modification in 2011 added theHamburg Wadden Sea National Park to the site, and the Danish part was added to in 2014.[37] Thestate of Bremen, covering part of theWeser River estuary, is not participating. Conservation efforts are coordinated by the Common Wadden Sea Secretariat, seated inWilhelmshaven.
The area bordering the Wadden Sea, including theFrisian islands and the mainlandcoastal marshes, is also called the Wadden Coast. In Germany the area is referred to as North Sea Coast (Nordseeküste). The embankedpolderlands andsaltmarshes in the Wadden Sea area – including theElbe Marshes – are referred to in Germany as North Sea coastal marshes (Nordseemarschen).
More recent are terms such as Waddenland, Wadden Sea area and Wadden Sea Region. The latter term is generally understood to include all coastal regions around the Wadden Sea that participate in the trilateral cooperation between Denmark, Germany and the Netherlands. The entire area is known for its rich cultural heritage, dating back to the Roman Iron Age and the Middle Ages, and largely coincides with the area internationally referred to asFrisia.[39] Between 2002 and 2023 stakeholder organizations and NGOs from the Wadden Sea Region cooperated in a platform or association called the Wadden Sea Forum (WSF).[40]
^"cultural-landscape"(PDF).waddensea-forum.org. Archived from the original on 24 September 2020. Retrieved4 November 2021.
^"Poster"(PDF). 1998.Archived(PDF) from the original on 2 May 2017. Retrieved4 November 2021.
^C. Michael Hogan (2011)."Wadden Sea". In P. Saundry; C. Cleveland (eds.).Encyclopedia of Earth. Washington DC: National Council for Science and the Environment.
^Scheffel, Richard L.; Wernet, Susan J., eds. (1980).Natural Wonders of the World. United States of America: Reader's Digest Association, Inc. pp. 408–409.ISBN0-89577-087-3.
^Fox-Kemper, B. et al. Ocean, Cryosphere and Sea Level Change. in Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (eds. Masson-Delmotte, V. et al.) 1211–1362 (Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2021).https://doi.org/10.1017/9781009157896.011.
^Pineda Leiva, D., Lorenz, M., Kösters, F. et al. Asymmetric morphodynamics of the Wadden Sea. Commun Earth Environ 6, 354 (2025).https://doi.org/10.1038/s43247-025-02340-y
^Nikulina, E.A.; U. Schmölcke (2015). "First archaeogenetic results verify the mid-Holocene occurrence of Dalmatian pelican Pelecanus crispus far out of present range".Journal of Avian Biology.46 (4):344–351.doi:10.1111/jav.00652.
^Borcherding, J.; M. Heynen; T. Jäger-Kleinicke; H. V. Winter; and R. Eckmann (2010). Re-establishment of the North Sea houting in the River Rhine. Fisheries Management and Ecology 17(3): 291–293.doi:10.1111/j.1365-2400.2009.00710.x
^Wolff W. J., 2000. The south-east North Sea: losses of vertebrate fauna during the past 2000 years. Biological Conservation 95: 209–21. accessed on 29 July 2014
^Linde Egberts and Meindert Schroor (ed.),Waddenland Outstanding. History, Landscape and Cultural Heritage of the Wadden Sea Region, Amsterdam 2018.
^"Wadden Sea Forum". Wadden Sea Forum e.V. 2023. Archived from the original on 20 November 2016. Retrieved22 April 2024.The Forum of the Wadden Sea Region, called Wadden Sea Forum (WSF) was an independent multi-stakeholder, multi-actor platform from Denmark, Germany and The Netherlands and contributed to an advanced and sustainable development.
