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Waidbacher, H. G. and G. Haidvogl (1998). Fish migration and fish passage facilities in the Danube: past and present. Pages 85-98 in M. Jungwirth, S. Schmultz and S. Weiss, eds. Fish Migration and Fish Bypasses, Fishing News Books, Vienna (Austria).

The Danube River flows 2850 km from its source in Germany to the Black Sea and historically contained no barriers to fish migration. Three species of diadromous sturgeon (Huso huso, Acipenser gueldenstaedtii, Acipenser stellatus) historically migrated from the Black Sea to the upper reaches of the Danube in Austria and Germany to spawn. However, beginning in the Middle Ages, fishing weirs were used to harvest sturgeon, sometimes blocking the entire river channel. Populations of upriver sturgeon were thus decimated long before permanent barriers to migration were constructed. Since the early 1970s, a hydropower facility at the Iron Gate in Romania (river km 931) has limited sturgeon to the lower river. Diadromous shad species (Pontic shad Alosa pontica and Caspian shad Alosa caspia spp.) also underwent historic migrations up into Hungary but were most abundant below the Iron Gate and thus still exist in some abundance. The middle and upper reaches of the main Danube channel were free of permanent migration barriers until 1927 when the Kachlet power plant was constructed; a fish ladder there demonstrated substantial movements of nase Chondrostoma nasus and barbel Barbus barbus as well as other species. This fishway, however, was the last built in the main channel for over 60 years, although within this time 29 power plants were constructed between Ulm, Germany and Vienna, Austria. Recently, two bypass systems have been built on the main channel of the Danube (Freudenau in Austria and Vohburg in Germany). The conservation of the rich Danubian ichthyofauna will largely depend on efforts to open up both the longitudinal and lateral connectivity of this alluvial river system.