All year around, the Rhine is habitat to many water fowl. From Lake Constance to the Rhine Delta the Rhine is equally an important rest and wintering area for water fowl.
The last inventory of water fowl along the entire course of the Rhine was drawn in 2000. Counts in November 1999 and in January and March 2000 amounted to all in all 2.1 million water fowl distributed across 42 species. (1995: 1 million distributed across 38 species). For 21 species abundance of international significance was stated. More than half of the water fowl were counted along the Lower Rhine downstream of Bonn. Additionally, in November, great numbers were recorded in the area of Lake Constance. The High, Upper and Middle Rhine mainly receive many water fowl species in the middle of the winter, in January.
Among the generally most frequent species are white fronted goose, mallard, tufted duck and coot. Herbivore species and species feeding on micro-organisms in water (benthivores) were most common. Herbivores such as white fronted goose and widgeon were above all found on the meadows along the Lower Rhine and on the foreshores of dikes in the delta. In shallow water areas along Lake Constance and along the Randmeeren, as well as in the Ijsselmeer/Markermeer water fowl preferring water plants, such as the mute swan and the red-crested pochard occurred in great numbers, just as benthivores such as tufted duck, pochard and scaup. This is due to the rich occurrence of the zebra mussel (Dreissena polymorpha) on which they feed. Piscivores form a considerably smaller group and are only represented by two important species – crested grebes and cormorants.