Zuider Zee, was a shallow bay of the north sea in the Northeast of Netherlands extending about 100km inland and about 50km wide having a depth of about 4-5m and a coastline of about 300km, it covered 5,000km^2.
In the 20 century majority of the Zuider Zee was cut off from the northern sea, allowing the inlet to become part of the Warden sea and the salt water inlet changed into a fresh water lake called the IJsselmeer
