Zooseston of the Vistula River section almost 340 km long was investigated in the years 1997/98. In 99 samples collected 90 species of rotifers, 16 cladocerans, 9 copepods and other animals belonging to: Harpacticoidea, Oligochaeta, Nematoda, Chironomidae, Odonata, Simulidae, Tardigrada and Coelenterata were found. Multiple regression analysis showed that the number of rotifers is significantly correlated with basic chemical indicators of water trophic state - phosphate, nitrate and nitrite as well as with the number of copepods which are usually predators. The numbers of copepods depends on the availability of possible prey, i.e. rotifers and cladocerans. Multiple regression confirmed known dependence of cladocerans from trophic conditions. Clustering of similarity matrices showed complex structure of sestonic assemblages on rhitral-potamal gradient additionally modified by hydrotechnical constructions. These constructions broke old river continuum. Ordination of sites gave complex pattern not only representing a simple gradient rithral - potamal but also all transient stages caused by hydrotechnical construction (large dam reservoir) or by inflows of polluted waters from the tributaries. Ecological meaning of principal component ordination (PC) for river zooseston assemblages is not simple and might be susceptible of various interpretations.
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