Groundwater flow, originating from the Biscayne Aquifer underlying lower southeastern Florida and extending beneath Biscayne Bay, is the only source of drinking water for about three million people from Boca Raton to the Keys. Historically, many freshwater springs occurred along the shoreline of the Bay, but many of these springs have ceased flowing as a result of the hydrological changes and are now the sources for saltwater intrusion into the Biscayne aquifer. Data from Biscayne National Park Long-Term Hydrographic Project shows that groundwater is seeping onto offshore coral reefs on a tidal cycle. This information is particularly important because it demonstrates that groundwater linkage between onshore sources of freshwater and offshore fully marine coral reef ecosystems. The data strongly suggests that pollution pumped into freshwater coastal aquifers will ultimately impact offshore coral reefs via this groundwater connection.