is often a dominant cladoceran zooplankton species in water bodies experiencing harmful cyanobacterial blooms. However, its relationship with toxin-producing algae remains largely unexplored. In this study, the feeding behavior of on colonial cyanobacteria and potentially toxic was investigated in a temperate, shallow, eutrophic lake. Liquid chromatographic analyses of phytoplankton marker pigments in gut content revealed that pigments characteristic of cyanobacteria (identified a zeaxanthin, echinenone, and canthaxanthin) comprised the majority of its diet. Among them, colonial cyanobacteria (marked by the pigment canthaxanthin) were the highly preferred food source despite their minor contribution to phytoplankton biomass. qPCR targeting genus-specific synthase genes, which are involved in microcystin biosynthesis, indicated that potentially toxic strains of were present in gut content throughout its temporal and spatial presence in the lake. The results suggest that the common small cladoceran in eutrophic waters, , has a close trophic interaction with colonial cyanobacteria (including ) and may represent an important vector for transferring toxigenic to the food web, even under conditions of low biomass in the lake water.