Jacob's Well is a perennial karst spring in the Texas Hill Country northwest of Wimberley, opening from the bed of Cypress Creek into a deep submerged cave system. Its circular mouth and clear water made it a well-known swimming spot, but the narrow, silty passages below are dangerous, and nine people died there between 1964 and 1984. Once powered by strong artesian flow from the Trinity Aquifer, the spring's discharge has been greatly reduced by groundwater pumping, and it first stopped flowing in recorded history in 2000. Protected land around the well has expanded, and the site now serves as both a natural landmark and a visible indicator of regional aquifer health.