The study focused on zooseston of the River Drawa, sampled downstream of the river’s outflow from Lake Grażyna (Site I), and that of a forest stream downstream of its outflow from Lake Krzywy Róg (Site II). The number of taxa at Site II was almost twice as high as that at Site I. The zooseston of the two sites shared as few as 24 taxa. The zooseston density at Site II was, on the average, almost 50 times higher than that at Site I, the biomass being 9 times that of Site I. Most abundant among crustaceans at Site I were Bosmina longirostris and nauplii, Polyarthra sp. being the most abundant rotifer. At Site II, the most abundant taxa included B. longirostris, Chydorus sphaericus, and nauplii as well as Keratella cochlearis and P. vulgaris. The highest biomass contributors at Site I were nematodes and chironomid larvae, B. longirostris, copepodids, and Asplanchna sp., the highest contributions to biomass at Site II being those of Polyarthra sp., K. cochlearis, Ascomorpha ecaudis, and Ch. sphaericus. Throughout the year, Site I witnessed the passage of 44 575 kg of zooseston, a quarter of that amount having passed Site II. Those amounts, when used as food, would be sufficient to support 8915 and 2165 kg non-predacious fish at Site I and II, respectively, i.e., equivalents of 4 457 510 and 1 082 520 fish fry individuals of 2 g individual weight.

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