The elevation of the so-called Bohemian mass began 17-18 million years ago in the Tertiary. At the end of the Tertiary, about 3 million years ago, the Danube found its present bed and followed a tectonic fault, i.e. a rupture edge. During the ice age, i.e. the Pleistocene, the Bohemian Massif rose again and at the same time the Danube was able to deepen strongly along the mentioned rupture edge. Thus it did not have to look for a new bed outside around the southern foothills of the Bavarian and Sauwald forests.
The Danube, probably the most interesting and probably most beautiful river in Europe, flows out of the brooks Brigach and Breg, which rise at over 1000 m above sea level in the Black Forest. In Passau, the Inn and the Danube, which are richer in water, join to form a mighty river. Nevertheless, the river is called the Danube.
The Danube remained untouched until the 19th century. A tangle of main and secondary arms, dead water and islands shaped its basin landscapes. The “first regulation of the Danube” from 1830 to 1880 created a uniform shipping channel, cut off the floodplain waters to a large extent from the main stream and thus significantly changed the water balance and landscape in the basin landscapes of the Danube valley. Reasons for the Danube regulations (power plants, …) were flood protection and safe navigation. In addition, the deepening of the river bed caused a drop in the groundwater level, which was initially positive for the cultivation of the fields.