Water filters which comprise a multitude of discrete filter media elements in a chamber require periodic cleaning. However, the elements tend to become adhered to one another and to the interior surface of the chamber. The invention provides a water filter for use with ponds, comprising a filter chamber for containing filter media, and a first movable cutting member provided substantially immediately adjacent the interior wall of the chamber for movement across the surface of the interior surface of the wall to break the adherence of filter media to the interior wall.