Tyre developed on a small, porous island, with restricted access to freshwater. The extraction of freshwater from beneath the island represents one of the ways the Tyrians could have reached self-sufficiency. Underground freshwater is contributed by rainwater and possibly by a deep, pressurized coastal aquifer below the sea. In order to document the geometry of this aquifer, a coring campaign was undertaken in 2023, revealing the spatial arrangement of permeable and impermeable layers under the peninsula of Tyre. The bioclastic sands that form the isthmus of Tyre are soaked in seawater. They rest on a saddle of impermeable clays between Tyre and the mainland. They protect an underlying body of freshwater from seawater contamination. The clay seal tappers against the calcarenitic ridge of Tyre, allowing freshwater to rise to the surface along the land-facing side of the island, feeding freshwater springs used since Antiquity.