We sampled phytoplankton, zooplankton, and alewivesAlosa pseudoharengusand measured water temperature in Lake Ontario during 1981–1986. Through the use of general linear regression models we then sought evidence of control of the eplimnetic zooplankton community (mid-July to mid-October) by producers, consumers, and temperature. Our measures of the zooplankton community were total biomass, cladoceran biomass, and the ratio of large to smallDaphniaspp. (D. galeata mendotaeandD. retrocurva). Zooplankton population variables assessed were abundance, egg ratio, and productivity. Through factor analysis, factors were created from the standardized, transformed independent variables for use in the regression analyses. Regression models showed significant inverse relationships (P< 0.05) between alewives andBosmina longirostris(abundance, production, and egg ratio),Ceriodaphnia lacustris(egg ratio), andDaphnia retrocurva(egg ratio).Bosmina longirostrisandD. retrocurvaegg ratios were inversely related to algae biomass (<20 μm), thus the smaller algae might be controlled in part by the zooplankton community. Production ofC. lacustriswas directly related to temperature, as was the production and abundance ofTropocyclops prasinus. The annual size-frequency distributions ofB. longirostrisandD. retrocurvawere inversely related to yearling alewife abundance and directly related to adult alewife abundance, which suggested that yearlings use a particulate-feeding mode on these zooplankton species more frequently than adults. We found no significant negative correlations among the zooplankton species, which suggested that interzooplankton predation and competition were not as important in structuring the community as were planktivory and temperature.