Abstract The Oak Island Money Pit has long been interpreted as a treasure repository. This paper presents a new hypothesis: the Money Pit is part of a complex tidal hydraulic system engineered in the late 17th to early 18th century. High-tide pressures, combined with a freshwater lens under the island, drive water into a timber-lined shaft. A half-mile red oak channel, extending from Smith’s Cove to a swamp relief zone, acts as a natural hydraulic ram. The system explains historical collapses, water intrusion, and the mysterious 175 × 100 ft stone pad. Evidence supports the shaft as a structurally engineered feature, stabilized by limited stone supports and stone-lined fingerling drains, rather than a conventional treasure hoard.