It flows through 10 European countries , which are Germany, Austria, Croatia, Hungary, Slovakia, Serbia, Romania, Bulgaria, Moldova and Ukraine, but its river basin includes 19 countries in total: Albania, Austria, Bosnia and Herzegovina, Bulgaria , Croatia, Czech Republic, Germany, Hungary, Italy, Macedonia, Moldova, Montenegro, Poland, Romania, Serbia, Slovakia, Slovenia, Switzerland and Ukraine. It passes through 4 capitals: Vienna (Austria), Budapest (Hungary), Bratislava (Slovakia) and Belgrade (Serbia).

It extends in central-eastern Europe from the Black Forest mountain range in Germany to its mouth at the Black Sea . The Brigach and Breg rivers are the tributaries that, when converging, give true origin to the Danube. Other important tributaries are the Inn, Prut, Iller, Isar, Raba, Drava and Morava rivers. The length of the river is estimated at about 2,860 kilometers, while its basin measures about 817,000 km2. Regarding the above, there are three subregions in the basin. The Upper Basin spans from the beginning of the river in Germany to Bratislava. In this section, the water runs at about 8 or 9 km/h, and the depth can be from 1 to 8 meters.

The Middle Basin is wider, exceeding 1.5 meters from side to side. It stretches from Bratislava to the Iron Gates, on the border between Serbia and Romania. The Lower Basin begins immediately. There the river flows slowly through a vast plain surrounded by Romanian plateaus and mountains. In the final section the Danube divides into three branches (Chilia, Sulina and St. George) that form a delta and flow into the Black Sea.

Discovering the origin of the Danube has not been easy. To this day, it is known to be older than the Rhine, another major river in Europe. In the Pleistocene, before the last ice age, the waters originating in the Alps and carrying water to the Rhine were part of the Urdonau , an ancient river that appears to predate today’s Danube. Subsequently, the waters of the Alps took another course and headed towards the Rhine, which they began to feed. The delta began to form about 6,500 years ago , as a result of the filling of an inlet of the Black Sea with earth transported by the river.

The Danube basin is a region full of life. Plains, forests, mountains, reedbeds, marshes, ponds and other biomes and ecosystems develop there, and in turn, provide habitat for plants and animals. Its delta contains the second largest wetland on the continent and the largest reedbed in the world. It is definitely a basin characterized by high biodiversity.

The river is home to some 7 endemic fish species (not found in other parts of the world), while the basin is home to more than 103 species of fish. Of them, sturgeons, the European eel ( Anguilla anguilla ) and the tarpon Alosa caspia, A. immaculata and A. maeotica . Some 88 species of freshwater mollusks and more than 18 species of amphibians also live in the basin. In addition, the delta is home to about 70 species of fish, of which about 45 are freshwater, 75 species of dragonflies, and 330 species of birds, including common pelicans (Pelecanus onocrotalus), herons, and pygmy cormorants ( Microcarbo pygmaeus ).

More than 83 million people live in the river basin who need water and the resources of the basin . Most depend on the water of the Danube to carry out their activities, for which more than 700 reservoirs and dams have been built. In past centuries it was an important communication route, and although today its navigation has been somewhat reduced, some sections continue to be key transport routes. Fishing, agriculture and tourism are other activities that focus on the river and its exploitation. However, due to the contamination of some sections of the course, fishing is no longer practiced as much.

Only 6.6 percent of the basin is protected , despite the fact that the river faces problems such as pollution due to waste dumped by industries, agriculture and human populations, gravel extraction and endangered species, among others. . Some of the most threatened species are the sturgeon, the common pelican, the Eurasian beaver ( Castor fiber ), the European kingfisher ( Alcedo atthis ) and the European pond turtle ( Emys orbicularis). The construction of the dams puts pressure on the fauna, since all human construction interferes with the natural space of the animals.