Seasonal changes of the plankton rotifer community in an eutrophic Czech reservoir were evaluated in relation to 46 environmental variables. To do this, data of rotifer abundance from three growing seasons (1993 - 1995) were analyzed. The seasonal dynamics of rotifers in all three years were characterized by two distinctive aspects: (1) the spring peak, with both maximum density and maximum species diversity, was dominated by Keratella cochlearis, K. hiemalis, K. quadrata and Polyarthra dolichoptera; (2) the summer-autumnal peak (or several lower peaks) of about half the intensity of the spring one, was composed mainly of Keratella cochlearis, Trichocerca similis and Polyarthra vulgaris. The separation between these two peaks coincided with the decline of phytoplankton and development of a clear-water phase in this reservoir. In redundancy analysis, species-abundance data for rotifers were related to all measured environmental variables. Date, abundance of Cyclops vicinus, total nitrogen, primary production, surface temperature, and density of heterotrophic nanoflagellates were identified as the most important variables. Partial redundancy analysis was used to assess the significance of pure and date-structured environmental factors influencing rotifers during the season. Date-structured environmental factors (such as physical and chemical variables, food, competition, and predation) significantly affected the rotifer community. This study shows that the rotifers in the reservoir are controlled by both abiotic and biotic factors.