The nature reserve "De Oostvaardersplassen" is an extensive marshland area with large landscape variations: from reed marshes to swamp forests and from grasslands to open water. The area is of a great importance to all birdlife. Both, breeding birds, migratory birds and wintering birds are observed. The natural site is situated in the newest polder of the Ijsselmeer area, Zuidelijk Flevoland, in the middle of what was once the Zuiderzee. The site lies about four metres below sea level. Since the first reclamation activities, the area has undergone a natural development. The land was never cultivated for agricultural or urban purposes as the rest of Zuidelijk Flevoland. A varied plant life, showing all the signs of a pioneer vegetation, developed on the clayey former seabed, now wholly or partially free of water.

The variegation of open water and covered higher ground attract all sorts of vegetation and thus also all sorts of birds and other animals. Most remarkable is the large number of breeding birds in spring and summer, and moulting and wintering birds in autumn and winter. The area is internationally acclaimed as "Wetland" and also as "Special Protected Area" (EC Bird Directive). Special facilities for the public have been constructed in the eastern part of the area, for example bird observation huts, signposted walking trails, observation sites and a visitors centre.