The Kalflack is one of the ten most important Old Rhine oxbow lakes on the Lower Rhine with typically marked floating leaf vegetation, reed zones, wetland tall herb fringe communities, intermittent pioneer mudbanks and small populations of softwoods. The water is a habitat for many fish species, including the rare spined loach.
The Kalflack is also a breeding habitat for many endangered bird species, including kingfishers and redshanks. Furthermore, the water is a winter habitat for whooper and Bewick's swans, shovellers and common teal as well as smews and goosanders.
The development goal is to conserve and improve an Old Rhine complex with a semi-natural structure and with typical river valley landscape elements (oxbow lake, softwood river meadow woodland). On the initiative of the Naturschutzzentrum im Kreis Kleve e. V. in cooperation with the Xanten-Kleve dyke association with finance from the Land NRW the construction of a fish ladder is planned in order to at least make it possible to periodically migrate between the Kalflack and the Rhine. The aim of this is to improve living conditions for the fish fauna. Some fish species use the oxbow lakes to spawn and as a nursery and then migrate to the Rhine, only to return to the oxbow lakes again for spawning a few years later.