Rivers: The river system in Austria is dominated by the four main rivers, the Danube, River (Donau), Inn, River, Salzach and Drau/Drava; 96 % of the entire Austrian territory is drained into the Danube. The only exceptions are Vorarlberg (drained for the most part into the Rhine), border areas in northwestern Lower Austria and northern Upper Austria (drained by the Lainsitz and other Vltava tributaries into the North Sea). Most of Austria's rivers are mountain rivers so that water quantity depends on the melting snows in the glacier regions. Many rivers have been dammed up to form lakes, which naturally regulates the outflow and debris. Forest lands also regulate the outflow and minimise the danger of floods. In general the lowest water levels are in winter (in flatter regions also in late summer), the highest after the spring thaw (for rivers in the high mountains in the summer) ( Flood). River navigation is limited almost completely to the Danube. Traffic on other rivers played a significant role before other methods of transportation (primarily the railway system) were developed. As the gradient is relatively high in many areas, Austria's rivers offer favourable conditions for building hydroelectric plants. 30 % of the hydraulic energy produced in Austria originates from storage power plants and 70 % from river power stations. Hydroelectric power meets around 70 % of Austria's electricity demand. In the 1980s and at the beginning of the 1990s the water quality of "extremely polluted" portions of Austria's rivers was improved; however, water quality still represents a serious problem in Austria. The most common causes of pollution are primarily waste water (discharges) from industries and households and "natural" discharges. The branches of industry which are responsible for most of the pollution of Austria's rivers are the chemical, sugar and food, pulps and paper industries, as well as the metal industry. The efficiency of municipal and private water treatment plants plays a decisive role, as does the percentage of waste water sources which have been connected with efficient treatment plants. Generally the rivers in Lower Austria, Vienna, Burgenland and in eastern Styria are more heavily polluted than in the other provinces. Examples of rivers with the poorest water quality standards II- III, III, and III- IV are the rivers Thaya, Kamp, Krems (Lower Austria), Pulkau, March/Morava, Traisen, Schwechat, Leitha and Danube (east of Vienna) as well as the Mur/Mura, Salzach and Inn (after flowing through the provincials capitals). With the exception of eastern Austria, the rivers with the best water quality standards, the categories I and I- II, are mainly smaller and medium-sized flowing bodies of water, and the upper reaches of larger rivers such as the Salzach, Mur, Drau, Gail and Gurk.
Literature#W. Katzmann and H. Schrom (eds.), Umweltreport Oesterreich, 21991; Oesterreichische Raumordnungskonferenz (ed.), OeROK-Atlas zur raeumlichen Entwicklung Oesterreichs, 1988; Federal Ministry of Agriculture and Forestry (ed.), Gewaesserschutzbericht 1993.