Abstract
Deep analysis of trophic state assessment methods has led to conclusion, that currently there is no universal methodology and existing methods are characterized by significant shortcomings. The approach proposed by the authors is different from generally used. Authors start from the assumption, that trophic state can be reflected by the state of biotic balance, which can be described by the values of Index of Trophic State. Researches were carried out in order to assess the trophic state of running waters and to estimate the limiting role of biogenic substances for eutrophication process development on the base of author's concept founded on above mentioned index.