The effects of different levels of nutrient input on the plankton community was investigated in a two-year controlled fertilization study of eight experimental ponds. There were four treatments, each replicated: a control, to which no fertilizer was added, and three levels of nutrient addition. Limnological parameters including phytoplankton and zooplankton densities were measured frequently during both summers and less frequently during the rest of the year. Inorganic nitrogen and phosphorus concentrations in the treated ponds increased. Phytoplankton and zooplankton density increased with treatment level but was variable. There was a limited relationship between the average chlorophyll a concentration per summer and the average cladoceran dry weight per summer. Above chlorophyll a concentrations greater than 60–70 mg/m3 other factors such as a pH zooplankton mortality effect, prevailed.