Being situated in the Wielkopolskie Lake District means that within the city limits of Poznań there is a dense network of rivers, apart from large natural lakes and numerous post-glacial hollows filled with water. There are also some 150 man-made reservoirs, which embellish the recreational areas, the biggest two being Malta and Rusałka. Apart from them, two other lakes are especially significant from ecological, recreational and economic point of view: Kierskie and Strzeszyńskie.