A hydrodynamic-oyster population model has been developed to assess the effect of different salinity regimes, produced by changes in freshwater inflow, on oyster populations in Galveston Bay, Texas. The population model includes the effects of environmental conditions, predators and (Perkinsus marinus), on oyster populations. The hydrodynamic model includes the effects of wind stress, river runoff, tides and oceanic exchange on the circulation of the Bay. Simulations obtained with the coupled models provide distributions of the total oyster population, market-sized individuals and disease prevalence and intensity that arise in response to differing freshwater inputs. Simulations for high, mean and low freshwater inflows will be presented and discussed in terms of the effects on oyster abundance and production