The Wadden Sea is a unique tidal area of wetlands situated along the Dutch, German and Danish coast between Den Helder in the Netherlands and Esbjerg in Denmark.
At high tide, the Wadden Sea area is flooded with water. Some hours later, at low tide, all the water streams back to the North Sea. These currents create deep channels and high sandbanks.
This makes the Wadden Sea a unique ecosystem where seals live amidst algae, seaweed, sea grass, lugworm, shellfish (mussels, shrimps and crabs), birds (ducks, gulls, sandpipers and waders) and fish such as plaice, flounder, dab etc.

The fact that the sandbanks in the Wadden Sea dry up during low tide is an important reason for the seals to stay, or to take up habitation, in the Wadden Sea. At low tide the animals can rest on the banks or lie in the sun. Sunlight produces vitamin D in the skin, which the seals need for moulting. Seals rest in groups on the sandbanks. This is safer, as there will always be one animal to discover approaching danger and alert the rest. However, it is also very important for social contacts and will eventually lead to mating, which takes place in the water. Young are born and nursed on the sandbanks. Within six hours a baby seal has to be able to swim, because the sandbank will flood with the next high tide. Seals have adjusted their lifestyle to this process.