What event in 1170 may have caused the creation of 5,000 km2 large shallow bay of the North Sea in the northwest of the Netherlands?
All Saints' Flood (1170) The All Saints' Flood of 1170 (Allerheiligenvloed) was a catastrophic flood in the Netherlands that took place in 1170. Large parts of the Northern Netherlands, and Holland territories were overflowed. This is the flood that created the Zuiderzee. "Lake Flevo" was once a fresh water lake, but after this flood a sea channel opened a connection from the North Sea into the lake through Creil Woods, and turned the lake into the salt-water sea known as the Zuiderzee. The Creiler Forest vanished forever under the waves.
Water board (Netherlands) Dutch water boards (Dutch: "waterschappen" or "hoogheemraadschappen" ) are regional government bodies charged with managing water barriers, waterways, water levels, water quality and sewage treatment in their respective regions. These regional water authorities are among the oldest forms of local government in the Netherlands, some of them having been founded in the 13th century.