text: The main driver of the concept is the beam effect, which indicates the influence of sections in very good ecological condition on sections in less good or rather poor condition with respect to their ecological status. There are two categories of beam effects which are biotic and abiotic. The biotic beam effect relies on the migration or drift of typical aquatic organisms; the abiotic beam effect refers to the transport of positive environmental conditions from one directed downstream. In general, the beam effect is not tied to the flow direction of the running water and can occur both upstream and downstream.
  In contrast, negative long-distance and vicinity effects cause the opposite effect to the positive beam effect, thus deteriorate the ecological condition of running waters. For instance, negative biotic effects are migration or drift of atypical aquatic organisms, that might have a negative effect on domestic species in their habitats; carry-over of fine sediments, material load or temperature influences are examples of negative abiotic effects on the ecological condition. Another negative effect is 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.