IJsselmeer

Lake in the Netherlands, area 1,217 sq km/470 sq mi. It was formed in 1932 after the Zuider Zee was cut off from the North Sea by a dike 32 km/20 mi long (the Afsluitdijk); it has been freshwater since 1944. The rivers Vecht, IJssel, and Zwatewater flow into the lake.

Four polders (reclaimed flatlands) have been recovered, primarily for agriculture. They are the Wieringermeer Polder 193 sq km/75 sq mi (1930); the Northeast Polder 469 sq km/181 sq mi (1942); the East Flevoland Polder 528 sq km/204 sq mi (1957); and the South Flevoland Polder 430 sq km/166 sq mi (1968).