Kudensee is a municipality in the Steinburg district in Schleswig-Holstein, and also the name of the largest lake in the Dithmarschen district. The Kudensee, with an area of 38.9 hectares, has been a nature reserve since 1935 and has been expanded to 172 hectares since 1992. The lake is the last shallow-water lake in the Elbe marshes and an important European bird sanctuary. It provides a habitat for numerous bird species, including the rare bittern, and serves as a resting place for many migratory birds.
The Kudensee is characterized by its extensive reed beds, remnants of marsh forest and willow bushes. The bottom of the lake consists of both soft mud and hard sand. Due to its shallow depth of a maximum of 1.2 meters, the lake has an almost uniform temperature and oxygen distribution, except when the ice is closed, which can be unfavorable for the fish. The fish species living in the lake include bream, white bream, roach, perch, ruffe, eel, pike and zander.