The Danube east of Vienna forms a living band through the last great landscape of riverine wetlands in central Europe. In 1996, the Donau-Auen National Park was established to preserve this sensitive ecosystem for future generations. The Danube and its wetlands are home to around 60 species of fish, more than 30 mammalian species and about 100 species of breeding birds. More than 800 plants of high order species form this water forest.
The approximately 48 kilometre-long and free-flowing stretch of the Danube between the Freudenau power plant in Vienna (river kilometre 1921.0) and the end of the Austrian-Slovakian border (river kilometre 1872.7) is a particular challenge. Here, where the river can still flow freely (without any man-made impediments),the consequences of the upstream dams of the Danube power plants are visible: the natural flow of gravel along the riverbed is interrupted as the Danube digs deeper and deeper into its riverbed causing both surface and groundwater levels to drop. During the course of the large-scale project to regulate the river in the 19th century, both riverbanks were reinforced with stone blocks, thus cutting off sidearm systems of the river from the main stream. This led to a decoupling between the river and the riparian forest, reinforced by falling water levels. In addition, fine sediment deposited during flood events also contributes to an increase of the surrounding areas from the river. Due to these slow but steady changes many typical riverine habitats have already been lost. Without countermeasures these negative developments will continue.
The Danube east of Vienna is also part of an international waterway connecting the North Sea to the Black Sea. The Main-Danube Canal was opened in 1992 and the Rhine-Main-Danube Waterway now connects a total of 14 European states by waterway. The total length between the mouth of the Danube into the Black Sea and the Rhine estuary into the North Sea is 3,504 kilometers.
In order to enable the Danube to play its role as an environmentally friendly transport alternative, shipping requires safe and economical waterway conditions. Critical shallow areas (fords) restrict the competitiveness of inland waterway vessels compared to lorries and railways, because cargo vessels often have to travel with less cargo in times of low water levels. A reduction of just ten centimeters in the water level means about 100 tons less cargo per vessel unit transported. Almost all the critical ford areas on the Austrian Danube stretch are located to the east of Vienna. The better utilisation of existing transport capacities on the Danube not only reduces greenhouse gases and pressure on road infrastructure (impervious surfaces), but also transport costs, thus safeguarding Austria as a business location.