The lower trophic linkages in lake plankton food webs are generally described as relatively simple, even accounting for the additional complexity of potential microbial looping. Crustacean zooplankton are frequently amalgamated into one trophic functional group as grazers of autotrophic production. The carbon stable isotope ratios for separated zooplankton species, particulate organic matter (POM) and phytoplankton from a number of lakes in Finland and the UK were analysed. These revealed greater complexity in trophic interactions than would otherwise be observed if the zooplankton had been represented by a mixed sample. Grazing zooplankton were usually depleted in 13C relative to the bulk POM on which they might feed, with 13C deviating by up to 17 There were no consistent differences between 13C values for copepods and cladocerans. Predatory cladocerans were generally enriched by greater than 1 compared to their putative prey. We suggest that care in separating the zooplankton species for stable isotope analysis may expose otherwise undetected sources of carbon and facilitate unravelling trophic links further up the food web.