The present day image of the Danube valley evolved only a few thousand years ago. After the last ice age, the water level of the Danube multiplied due to the melting and it cut a wide, deep valley through the mountains, forming the beautiful scenery of the Danube Bend. By depositing its load the Danube created islands in the area of the National park, such as the partly protected Szentendre Island.

The Danube is home for rare fish, such as the Zingel [Zingel zingel], the Streber [Zingel streber] and Striped Ruffe [Gymnocephalus schraetser]. All three species live in the main river branch as they require fast flowing waters. They are active at night, searching for food in shallow waters. Their diet is composed of small animals or of organic debris drifted by the water, which they search for at the bottom of the river bed, on pebbles or between the water and pebbles. The spawn also develops in shallow, high-drifting water.

The most valuable species living in the Danube are those which evolved in the Danube or its side stream tributaries, and their present expansion is mainly limited to these waters therefore the preservation of these species is only possible in these waters. As a result of dredging in the Danube these species suffered serious damage. Further regulatory projects may lead to the disappearance of these species from this section of the river.