Environmental requirements for adult bay scallops (Argopecten irradians concentricus) in Tampa Bay were assessed from field and laboratory studies conducted from June through October 1992. These requirements were based on correlations of scallop growth, mortality and reproduction with species-relevant measurements of water quality. Under laboratory conditions, bay scallops were able to survive low dissolved oxygen (2 mg/L) for six hours at 25 deg C. As water temperature increased, bay scallops were less tolerant of low dissolved oxygen. General water quality in Tampa Bay, with respect to chlorophyll a, turbidity and nutrients, has been steadily improving since 1980. The ability of bay scallops to grow and spawn in the waters of lower and middle Tampa Bay reflects the improvements in water quality observed over this period.