The Bay of Fundy has among the highest tides globally, and its mega-tidal conditions drive high exchanges of fresh- and salt-water in surface estuaries. To examine potentially related subsurface exchange in coastal aquifers (�subterranean estuaries�), we present new results from field and modeling investigations of ocean-aquifer mixing at two sites along the Fundy coastline in Nova Scotia: Wolfville and Advocate Harbour. Field investigations in the Wolfville dykelands and aquifer reveal pronounced tidal oscillations in groundwater levels at great depth and distances inland, and high variability in ground resistivity attributed to tidal variations in porewater salinity. HydroGeoSphere simulations of coupled surface and subsurface flow and solute transport for this site reveal that sea-level rise will likely disturb the saltwater-freshwater transition zone and threaten the town�s drinking water, while surge-driven overtopping of dykes can salinize critical agricultural fields. Field data from Advocate Harbour across the Minas Basin from Wolfville indicate that the tides drive intensive aquifer-ocean mixing along a cobble beach as supported by strong tidal oscillations in groundwater levels and high rates (e.g., up to 1.8 m/day) of submarine groundwater discharge measured in seepage meters and via interpretation of time series of radium concentrations. These field and model investigations of coastal aquifers reveal extreme groundwater exchange along the Bay of Fundy that warrants more consideration given the emergence of Nova Scotia�s first Coastal Protection Act and recent provincial dyke management decisions in light of ongoing marine climate change.