White perch (Morone americana) became established in Missisquoi Bay, Lake Champlain in the mid 1990s. Since that time, cyanobacteria blooms have become common in summer. Although introduced planktivorous fish often impact plankton communities through a reduction in Daphnia density, such effects can be difficult to predict in an opportunistic species such as white perch. In this study, we examined the extent of zooplanktivory exhibited by adult white perch in Missisquoi Bay. Adult white perch were collected from Missisquoi Bay on ten dates in spring and summer of 2005. White perch diet consisted of large numbers of Daphnia on dates when Daphnia densities exceeded 20 individuals/L and when Daphnia comprised more than 50% of the zooplankton assemblage. When Daphnia densities were below these threshold values, adult white perch diet consisted predominantly of benthic prey. Our results show that white perch feed on large numbers of Daphnia in Missisquoi Bay and select Daphnia over other zooplankton taxa when they are abundant. It is likely that adult white perch grazing in Missisquoi Bay has contributed to a reduction in Daphnia density which in turn may be contributing to summertime cyanobacteria dominance in this bay.