text: A beam origin (also beam source) is a river section that is in very good ecological condition. The river section may not necessarily be located in the main course but side waters. On the one hand, it shows structural, hydrological and hydraulic quality close to nature; on the other hand, it is the natural habitat of typical organisms that can drift and migrate to other sections. If a beam source only meets the prerequisites for an abiotic beam effect it is called a potential beam origin and it is assumed that in the long-term a typical inventory of species can be formed.