What is "marsdiep"

The Marsdiep is a deep tide-race between Den Helder and Texel in the Netherlands, and running southwards between sandbanks. That gap connects the North Sea and the Waddenzee.

Around 1000 AD and before, much of the modern Waddenzee and IJsselmeer was land and the Marsdiep was an ordinary river. An early form of its name is Maresdeop, a name probably related to modern Dutch moerasdiep ("swamp deep"). During the All Saints' Flood (1170) the sea broke through the original dune barrier and created the channel. For more information see Wieringen.

The Marsdiep was in the age of sail in English called the Texel, in distinction from the island of Texel.