The main idea behind the formation of polders was agricultural production. At present polders are used to realize more and more non-agricultural functions. Some polders can be renaturalized. Polder water-melioration systems determine settlement and economic activities in the polders including farming. They are formed by embankments, pump stations, canals and reservoirs, drain ditch networks, irrigation devices and roads which are indispensable for the system to work. The aim of the work is identification and estimation of the functions of polder areas using the example of Druzno Lake basin in Żuławy region.