EN
The paper describes and compares various (chemical and biological) methods used in Poland for lotic water quality assessment; included are methods which have not been formally approved yet. Based on ecological surveys made in 1996-1998, a quality assessment of water of rivers Tywa and Rurzyca is presented. The assessment allows to conclude that application of a single method leads to a serious misrepresentation of the lotic biota. In both rivers there were sections the water of which, when assessed with physico-chemical methods, appeared much different than when assessed with biological methods in both seasons of studies.