Zuider Zee[zī′dər zē′; Du zo̵i′dər zā′]
former arm of the North Sea, which extended into the Netherlands: its S section was shut off from the North Sea by dikes
A former shallow inlet of the North Sea in northeast Netherlands. Originally a lake, it was joined with the North Sea by heavy flooding. A dike, completed in 1932, turned the southern section into the Ijsselmeer, which has largely been reclaimed for agriculture.