The waters off Elliot Key, within Biscayne National Park (BNP) in the United States, contain some of the longest lived specimens of Montastraea faveolata in the Caribbean. Previously we have noticed an inconsistency between measured water temperatures and temperatures estimated using the Sr/Ca and the 18O of the coral skeletons. This inconsistency is a result of the fact that the reefs are influenced by evaporated water emanating from Biscayne Bay as well as groundwater from the adjacent mainland. The water from Biscayne Bay is elevated in 18O, which influences the reefs to a greater extent during the summer thereby depressing the 18O amplitude of the skeleton. At the same time the ground and surface waters are highly elevated in calcium, resulting in lower than expected Sr/Ca ratios. This enhances the range of Sr/Ca in the corals. By combining these two proxies with measured SST data, it is possible to use the corals as proxies of the amount of freshwater discharge from the adjacent mainland. It is possible to distinguish surface water from ground water using the Ba/Ca ratio. Surface waters have elevated Ba/Ca ratios compared to ground water, and therefore distinctions between surface discharge and groundwater discharge can be assessed using this ratio in the coral skeletons. In this presentation we present (i) high resolution reconstructions (>40 samples per year) over the past 50 years from three sites in Biscayne National Park, and (ii) a lower resolution record extending back to ~1750.