Lake Rotorua is a eutrophic polymictic lake in the centre of the North Island, New Zealand. Three studies of its crustacean zooplankton, in 1955–56, 1967–69, and 1994–95 have been made. Despite increased eutrophication since the first study, species composition has not changed: the calanoid copepod,Calamoecia lucasi, dominates for much of the year andBosminacf.meridionalisandCerio‐daphniacf.dubiaare the only limnetic cladocerans. Comparison of their annual cycles in abundance between the studies show little regularity in the seasonal patterns, suggesting that stochastic events, such as storms, may be the most important controlling factors through their effects on food levels.