The problem of quality assessment of surface waters as exemplified by rivers Tywa and Rurzyca

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.