Distribution of hydrobionts over the entire area of a water body (watercourse) or in its individual sections. It is expressed as an indicator of the frequency of occurrence of organisms on a certain area as a percentage of all individuals located on the entire area of the reservoir.

The distribution of fish in water bodies is determined by a complex of abiotic and biotic environmental factors, most of which have a universal effect on the process of fish distribution in reservoirs and watercourses. At the same time, only a few external factors - first and foremost current and, in some cases, temperature - are specific, characteristic of certain types of water bodies. The distribution of fish is a dynamic process and its daily and seasonal cycles can be observed everywhere.