Zuyder Zee, Or Zuider Zee (South Sea), a bay or gulf on the coast of Holland, so named because it is separated by the islands of Texel, Vlieland, Ter Schelling, and Ameland from the North sea or German ocean. It is bounded N. W. and N. by the islands already named, E. by Friesland and Overyssel, S. E. by Gelderland, and S. and W. by Utrecht and North Holland; length from N. to S. about 80 m., greatest breadth about 35 m. A projecting peninsula partially divides it near the middle, S. of which it expands to its greatest width. At its S. W. extremity an arm called the Y branches off and extends into the province of North Holland; it is navigable by vessels of considerable size, and forms the harbor of Amsterdam. Formerly this arm extended W. to within a few miles of the North sea, but most of it has recently been drained. The shores of the Zuyder Zee on the east and southeast are several feet above the sea level, but those on the west are only protected from inundation by strong dikes. The sea is generally deep enough for vessels drawing not over 15 or 18 ft., but navigation is obstructed by shoals.

The most important tributary is the Yssel. - In the time of the Romans the Zuvder Zee was a low swampy lake called Flevo, and communicated with the North sea by a stream bearing the name of Flevum. In 1219 a severe inundation took place in consequence of continued N. W. winds, broke clown the dikes, and made considerable encroachments on the land. In 1282 a still more terrible one occurred, which submerged 72 towns and villages and drowned nearly 100,000 persons. By this calamity it became an arm of the sea, and attained its present dimensions. Investigations have recently been made at the expense of the Dutch government with a view to the drainage of most of the southern half of the sea, and the state commission has pronounced the scheme practicable. It is proposed to construct an enormous dike, extending from Enkhuisen on the W. shore to the island of Urk, and thence to the E. shore at Kampen, a total distance of about 25 m. The basin thus enclosed would embrace nearly 800 sq. m. or about 500,000 acres, an area nearly equal to that of the province of Limburg. The bottom consists of thick beds of rich alluvium traversed by great banks of sand, one of which forms the line of the projected dike, and would serve as its foundation.

Nearly the whole of the land, it is thought, would be suitable for cultivation. The plan contemplates a network of canals and watercourses, and the time required for the whole undertaking is variously estimated at from 12 to 20 years, and the cost in round numbers at about $50,000,000. - See Visite aux villes mortes du Zuyderzee, by Henri Havard (Paris, 1875; English translation by Annie Wood, London, 1875), and Le dessechement du Zuyderzee, by George Herelle, in the Revue des Deux Mondes, Nov. 15, 1875.