The investigated reservoirs of fish farms, 76 taxonomic units of zooplankton, represented by colloquials (Rotatoria) and crustaceans (Crustacea), have been identified. As part of the dominant complex, representatives of the genera Asplanchna, Brachionus (Rotatoria), Ceriodaphnia, Daphnia (Cladocera), Acanthocyclops, Eudiaptomus (Copepoda) prevailed. When May to September, indicators of zooplankton development were 118.73–348.37 thousand ind./m³ - by the number of organisms and 6.08–9.95 g/m³ — by biomass. The basis of phytoplankton has consisted of green, diatoms, eugenic and blue-green algae with a predominance of the genera Scenedesmus, Euglena, Navicula, Pediastrum, Peridinium, Oscillatoria, Microcystis. The average seasonal values of phytoplankton fluctuated within the limits of 39.15–169.87 million cells/dm³ – by the number and 4.69–13.86 mg/dm³ — for biomass. Zoobenthos of the studied reservoirs were represented by larvae of Chironomidae and Oligochaeta. The average seasonal numbers of zoobenthos in the ponds of the farms were in the range of 246.05–367.18 ind./m², biomass 1.74–1.92 g/m². According to the results of the epizootic monitoring in the fish farms of the Lviv region, the invasiveness of the carp by ectoparasites Lernaea cyprinacea and Dactylogyrus vastator is established. The disease was recorded as mono- and associative invasions. The extensiveness of the invasion (of yearlings carp lernaea in the growing ponds was 10–35% (intensity of invasion — 1.67–3.43 sp.), dactylogyruses — 10–50% (II — 4.2–11.6 sp.). Mixed invasion L. cyprinacea and D.vastator are found in 20-35% of yearlings carp (II lernaea — 1.75–2.83 sp., dactylogyruses — 6.75–11.33 sp.).  The highest invasibility of yearlings carp with ectoparasites in the ponds was established during July–August.