Zuider Zee (Zoi'der Zay; 'southern Sea,' as opposed to the North Sea), a large gulf penetrating 60 miles into the Netherlands, and 210 miles in circu?nference. The islands Texel, Vlieland, Terschelling, Ameland, and Schiermon-nikoog, reaching in a chain across its entrance, are the remains of the former coast-line, which in 1282 was broken by the sea, the waters overflowing the low lands between Friesland and North Holland, uniting with the small inland lake Flevo, and forming the present Zuider Zee.

In it lie the islands Wieringen, Urk, Schok-land, and Marken. From the south-west of the Zuider Zee a long narrow arm, called the Y (pronounced I), formerly ran nearly due west, through the peninsula of Holland. A strong sea-dyke and locks have been constructed to cut off the Zuider Zee from the Y, through which a broad ship-canal has been made between Amsterdam and the North Sea. On both sides of the new canal the Y has been drained and turned into about 12,000 acres of rich land. The new waterway was formally opened by the king in 1876. In 1892-94 a royal commission drew up a scheme to drain the Zee and reclaim some 750 sq. m. at a cost of 26,000,000. See Havard, Dead Cities of the Zuyder Zee (trans. 1876).