given by the so-called colmation, which is the accumulation of fine particles on gravel deposits. Since the pores are used by organisms for spawning, over time the sediments cut off the oxygen supply, cover the gravels with a solid layer and destroy the habitat of local species. Ecological condition The definition of a good ecological status is a matter of interpretation. For member states of the European Union, the Water Framework Directive defines two different ecological target states, which are the good ecological status and the good ecological potential. The good ecological status refers to a natural body of surface water, whereas the good ecological potential specifically relates to a heavily modified or even artificial body of water that was created by human activity. Typical indicators Typical indicators for the evaluation of the ecological quality are the abundances of fish, macrozoobenthos, macrophytes and phytobenthos, and the number of type-specific taxa. Criteria to further classify the ecological status of river sections can be found in the European Directive or in country-specific guidelines. Components Beam origin 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. Beam path A beam path is a river section of low ecological condition that borders on sections of higher ecological potential. An enhancing beam path is a type of beam path into which organisms of a nearby beam source can migrate or are at least temporarily settle. Furthermore, typical organisms can only drift or migrate through the beam path, which is then called a transit beam path. In a beam path a biocenosis can be established which is only possible due to the presence of adjacent beam origins. Stepping stone A stepping stone is a morphological element that allows organisms to either migrate and settle or drift though the river section. It does not necessarily have to be a stone or a group of