The filtering capacity of dense bivalve populations can exert strong controls on phytoplankton biomass, leading to increased water clarity and reduced hypoxia. Bivalves, particularly oysters, therefore are the focus of many restoration efforts and ecosystem-based management plans. The hypothesis is tested that oysters have feeding access to the classic major phytoplankton bloom of the year in winter–spring. Jamaica Bay is a highly eutrophic urban estuary where oyster restoration is being considered as a means to improve water quality. Strong winter–spring and summer phytoplankton blooms occur in Jamaica Bay, and oyster feeding rates and oxygen consumption were examined to see if oysters would be able to feed during both seasonal pulses of phytoplankton. Temperature-related feeding rates were found to vary to the degree that feeding did not occur at the cold temperatures that exist during the winter–spring blooms. Indeed, feeding rate and proportion feeding were found to be zero at 10°C, which corresponds to March–April. But feeding would be vigorous in late spring and summer. Oysters, therefore, do not have the ability to regulate a major fraction of phytoplankton during the year in Jamaica Bay and likely in the rest of the mid-Atlantic states region and New England. Feeding rates are much higher during the time of the summer blooms, and oysters in shallow well-mixed waters would, therefore, have access to feeding and possibly control of phytoplankton biomass at this time.