Strong oscillations in the rotifer community are frequently observed in eutrophic lakes, where rotifers are important components of the zooplankton community. Manipulations with increased level of fertilizers, presence or absence of fish, abundances of competitors (cladocerans) and predators (Asplanchna) were performed in polyethylene-enclosures. The experiments provided evidence for pure eutrophication effects (e.g. elevated pH) and predation from Asplanchna as the main controlling factors. The influence from potential competitors such as Daphnia and Bosmina was found to be of less importance, at least during these short-term experiments.