G. Evelyn Hutchinson proposed that external control by climate limits the fundamental productivity and the possible diversity of ecological communities. These climatic drivers are currently changing as a result of human activity, which may herald a shift in the influence of climate on global ecosystems. Long-term records reveal a reduction in ice cover on northern lakes over the last several centuries. Hence, we explore whether inter-annual climatic variability, represented by ice cover, influences the productivity and diversity of zooplankton communities in long-term datasets for five lakes in Northern Wisconsin. We used a multilevel modeling approach to test three predictions: (1) density will increase, (2) diversity will increase, and (3) community composition will be altered. We found an inverse relationship between ice-off date and annual zooplankton density. Daphnia density, for example, was inversely related to ice-off date, with 10-fold variability across the gradient of ice-off dates in Northern Wisconsin. In contrast, we did not observe a consistent shift in diversity or community structure. Thus, from ice cover records of northern lakes we found support for Hutchinson's idea that external climatic forces may regulate aquatic productivity; however, the response was numeric and we did not find evidence that lakes moved closer to maximum diversity on an inter-annual scale.