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2010 Phytoplankton production is a basic process in aquatic ecosystems that converts inorganic carbon into organic matter and provides an important indicator of trophic state. The City of Tampa Bay Study Group maintains a 32 year long monthly record of phytoplankton production rates and biomass (chlorophyll-a) in Hillsborough Bay (HB) and Middle Tampa Bay (MTB), and a recent record during the last nine years for Old Tampa Bay (OTB). Production is measured using the classic in situ 14C method with samples incubated vertically in the water column. Annual production rates during the most recent decade are about 410gCm-2 for HB, 350gCm-2 for MTB, and 390gCm-2 for OTB. The current rates for the two former bay segments are near half the rates measured during 1980-1985. Reductions in biomass have been greater; current HB and MTB concentrations are near 70 % lower than those measured during 1980-1985. Water column averaged chlorophyll-a concentrations during the most recent decade are about 10mgm-3 for HB, 5.8mgm-3 for MTB, and 6.3mgm-3 for OTB. The decreases in production an