Midsummer zooplankton community structures of 50 Adirondack lakes were evaluated in relation to dominant vertebrate and invertebrate predators and selected limnological parameters. The most important factors structuring zooplankton grazer communities were extracted in a principal components analysis. The interaction of acidity status and vertebrate planktivore abundance explains the variation in lake scores for the first principal component. The second principal component was related to predation, while the third was related to lake trophic status and humic influence. The interaction of water quality and predator abundance structures grazer communities of Adirondack lakes.