Background The River Traisen, one of the largest Danube tributaries in Lower Austria, runs for 7.5 km as a regulated, straight-line channel through the Natura 2000 site, Tullnfelder Donau-Auen. This site is the largest alluvial forest in Austria. However, the River Traisen is a heavily modified water body following the construction of the hydropower plant, Altenwörth, in 1976. The regulated river is missing aquatic and terrestrial habitats that are usually found on flood plains. The connection between the river and the surrounding riparian forest is cut off. This situation leads to an unfavourable conservation status for the whole Natura 2000 site. High waters of the regulated Traisen rarely reach the surrounding habitats because of flood protection dams. Objectives The main project objectives are to: Create a new and dynamic river bed; Restore large-scale flooding zones to restore and maintain the alluvial forest priority habitat type 91E0 with typical white willow woods; Link numerous floodplain waters to the new main river; Create a free passage for fish and other water species. The project is expected to implement its measures on a 12.5 km stretch of the meandering River Traisen with dynamic banks and natural riparian forest areas. It is also expected to create a new running water habitat at mean-flow of some 69 ha, where dynamic riparian development can take place. The project foresees the creation of: Various natural river structures in the riparian area between water and land; Some 82 ha of frequently flooded areas, which are suitable for the restoration of the priority habitat type of white willow woods (91E0). It will Increase this habitat type in the target area from 6% to approximately 100%; Stagnant water zones to enrich the water variety of the floodplain by 12 ha; Fish passable cross-links on the floodplain area and various existing water bodies with the new River Traisen and the Danube. This will make permanent fish migration possible in the new River Traisen. At least 40 fish species will benefit from this measure, of which 25 species are listed in annex II of the Habitats Directive.