This study investigated three earth fish ponds fed with biologically treated wastewater from the treatment plant in Olsztynek. The ponds were stocked with the following fish species with a varied age structure: common carp (Cyprinus carpio), tench (Tinca tinca), European pike-perch (Sander lucioperca), and roach (Rutilus rutilus). Zooplankton samples were collected once a month, from April to October 2007. Rotatoria were the most diverse and the most abundant zooplankton community. The zooplankton biomass in all ponds was dominated by crustaceans, including such species as Keratella cochlearis, Keratella quadrata, Polyarthra longiremis, Brachionus angularis, young forms of Copepoda (nauplii and copepodites), as well as Daphnia longispina and Thermocyclops crassus. The greatest faunal similarities between the analyzed zooplankton groups were determined in ponds 1 and 2, while the greatest differences were noted between ponds 2 and 3. The structure and dynamics of zooplankton changes in the investigated ponds were determined mostly by trophic relationships and interspecies interactions, while fish predation pressure supported greater species diversity and its reinstatement.