By nature, the Rhine flowed north of Karlsruhe in large loops and loops through its lowlands and repeatedly shifted its course, especially during floods. In the course of Tulla's correction of the Upper Rhine, such a Rhine loop was pierced approximately in the middle near Ketsch from 1833 to 1845. This created the Ketsch Rhine Island, which is enclosed by the semi-circular remnant of the Rhine bend - today's Altrhein - and the straightened Rhine bed. The Altrhein is still connected to the Rhine today and flows freely. It is still flooded during high water and is thus one of the last large-scale and natural floodplains on the Upper Rhine. Despite all human interventions, the Ketsch Rhine Island harbours a near-natural floodplain landscape with high ecological value. Natural and near-natural floodplain forests, water bodies and wet sloughs as well as dry gravel ridges offer a distinctive structural diversity and thus habitat for a rich flora and fauna. So far, well over 500 species have been identified, many of which are rare or endangered.
The nature reserve "Ketscher Rheininsel" was designated in 1950 and extended in 1983. It covers an area of 490 ha. According to the ordinance, the purpose of protection is the preservation of a near-natural Rhine floodplain landscape with typical floodplain plant communities as a habitat for endangered plant and animal species. The nature reserve is part of the bird sanctuary "Rheinniederung Altlußheim-Mannheim" and the FFH area "Rheinniederung von Philippsburg bis Mannheim". The Ketsch Rhine Island is therefore not only of supra-regional but also of European significance.
