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The nutrient levels, notably phosphorus and nitrogen, found in the Danube River and its major tributaries hold significant international importance. This is because they directly contribute to the phenomenon of eutrophication in both the river itself and the Black Sea. Historical trend analysis of nutrient river loads over the past decades shows a significant reduction in the transported nutrient fluxes to the Black Sea. Overall nutrient emissions declined by 30% (nitrogen) and 50% (phosphorus) in the last 15 years. However, the current long-term fluxes are still considerably higher than those of the early 1960ies which represent river loads under low pressures, indicating a further load reduction potential that might be exploited for the benefit of the Black Sea. Nevertheless, in the last 5-10 years the measured loads are rather low and close to the Black Sea targets indicating significant water quality improvement.

The floodplains and wetlands of the Danube basin are uniquely valuable ecosystems in global terms, although few areas are still in their natural or near-natural state.

The Danube River is seeing an influx of new non-native species, stemming from the increasing interconnections with various European and global water bodies via canals and other waterways designed to facilitate navigation. It is currently believed that alien species are very likely to become even more significant in the future, as the importance of the Danube as an international waterway increases.

The habitats created by the Danube and its tributaries host a unique mix of species. But many habitats are degraded by man-made changes to the river profile and width, water depth and flow velocity following the construction of dams, weirs and canals. Many migratory fish including sturgeon species and the Danube Salmon are endangered or close to extinction by being disconnected from their spawning grounds and habitats or by being over-exploited.

Floods are natural phenomena. They can, however, turn into disasters causing widespread damage, health problems and even deaths. This is especially the case where rivers have been cut off from their natural floodplains, are confined to man-made channels, and where houses and industrial sites have been constructed in areas that are naturally liable to flooding.

A river does not end at its bank. The Danube and its tributaries form many diverse riverine habitats, including intricate networks of water bodies, creeks and channels, floodplain forests, water meadows, lakes, gravel islands, sandy banks and the unique delta habitats by the shores of the Black Sea.

The Danube and its tributaries host a variety of fascinating and diverse ecological territories with many unique plants and animals. The rich and unique biodiversity and riverine habitats have been under severe pressure due to human activities for centuries. However, today the protection of environment and biodiversity is on the political agenda of the different Danubian States.

Since the 16th century, people have been changing the natural course of the rivers in the Danube River Basin, mainly for flood defence, hydropower generation and navigation. All these changes affect the ecological quality of the rivers. Changes in the depth or width of a river typically reduce flow rates, interrupting natural sediment transportation as well as the migration routes of animals.

Water quality in the Danube has improved over the years, but there is still much work to be done to meet the region’s goals for water status. To improve the water quality, an ambitious programme of measures for the whole Danube River Basin District has been agreed under the EU WFD. To assess trends in water quality, the ICPDR oversees the TransNational Monitoring Network (TNMN). The network carefully monitors physical, chemical and biological conditions in the Danube and its tributaries, and provides in TNMN Yearbooks an annual overview of pollution levels as well as long term trends for water quality in the basin.

Many people consider droughts to be rare, but in fact they are a normal and recurrent feature of the climate. Drought events are regional phenomena, affecting transnational water management. Unfortunately, droughts have a high damage potential: economic losses, ecological damages, and implications on human health.