A polder's a low-lying tract of land enclosed by embankments known as dikes, that forms an artificial hydrological entity, meaning it's no connection with outside water other than through manually-operated devices. There're three types of polder: Land reclaimed from a body of water, such as a lake or the sea bed. Flood plains separated from the sea or river by a dike. Marshes separated from the surrounding water by a dike and consequently drained. The ground level in drained marshes subsides… (More on Polder)