Re-naturalisation of polder areas

A polder is a low-lying tract of land enclosed by embankments (known as dikes) whose altitude is usually below sea level. It forms an artificial hydrological entity, meaning it has no connection with outside water other than through manually operated devices. The re-naturalisation, or depoldering, of polders involves enhancing their sub-natural characteristics to allow better water storage in watercourses inside the polder and increase biodiversity.

Depoldering is the opposite of human development and aims to reopen the polder to marine intrusion for renaturation or ecological restoration purposes. From the 1980s to the 2000s, the amount of depoldering undertaken tripled, and the areas involved became increasingly vast. There are even plans to return entire reclaimed islands to the sea.