The primary outcome of this study has been to increase the understanding of the environmental drivers that influence the southern NSW Sydney rock oyster (SRO) industry, in particular in the Clyde and Crookhaven/Shoalhaven estuaries and to identify some of the factors that limit the production of SRO. Increased amounts of nitrogen and organic carbon are delivered by increased river flows following rain events and these were found to significantly enhance oyster growth in the two south NSW estuaries. During normal and/or dry conditions, the estuaries were nitrogen-limited suppressing primary production and, potentially, oyster growth. On the other hand, during heavy rain periods, large amounts of nitrogen entered the estuaries, which then became phosphorus-limited. Optimally an intermediate level of Nitrogen:Phosphorus ratio is desired for enhancing SRO production in the south coast of NSW so that neither nutrient is limiting.