The Holzhafen nature reserve in Billwerder Bay has a total size of approx. 80 hectares and, with its extensive, tidal areas of water and tidal flats next to the Mühlenberger Loch, is the most important resting area for migratory bird species such as the shoveler, teal and shelduck in Hamburg an important function as a feeding, spawning and growing area for fish. Part of the protected area is also a tidal bank area, which was restored in 2008 by back dikes as a nature conservation law compensation measure and now extends the wooden harbor by approx. 20 ha to the south. This area has a specialized inventory of species adapted to the dynamics of the tides. Here you can find plant species such as the lancet-leaved frog spoon, spreading ragwort or hemlock water fennel, which are threatened with extinction in Hamburg.