Lauwersmeer is a man-made lake in the north of the Netherlands, on the border of the provinces of Groningen and Friesland. The lake was formed on 1969-05-23, when the dike between the bay called "Lauwers Sea" and the Wadden Sea was closed.On the eastern shores of the Lauwersmeer is the Marnewaard, an exercise area of the Royal Netherlands Army.
The 13 kilometers (8.1 mi) long dike has a sluices and a canal lock. A new harbour called Lauwersoog was built part-way along the dike. Final enclosure and separation from the Wadden Sea took place on 25 May 1969;since then it has been called Lauwersmeer.New flora and fauna appeared as the Lauwerszee gradually became a freshwater lake, and to protect this new and young nature area, it was decided (12 November 2003) to designate the Lauwersmeer as a national park.