Jacob's Well is a perennial karstic spring in the Texas Hill Country flowing from the bed of Cypress Creek, located northwest of Wimberley, Texas. The twelve foot (four meter) diameter mouth of the spring serves as a popular swimming spot for the local land owners whose properties adjoin Cypress Creek. From the opening in the creek bed, Jacob's Well cave descends vertically for about thirty feet (ten meters), then continues downward at an angle through a series of silted chambers separated by narrow restrictions, finally reaching a depth of one hundred and twenty feet (forty meters). Until the modern era, the Trinity Aquifer-fed natural artesian spring gushed water from the mouth of the cave, with a measured flow in 1924 of one hundred and seventy gallons per second (six hundred and forty liters per second) discharging six feet (two meters) into the air. The spring is the greatest source of water recharging the Edwards Aquifer.
Due to development in the area, the level of the Trinity Aquifer has dropped affecting the flow of water through Jacob's Well. In the modern era, what remains visible of the spring is a faint ripple on the surface of Cypress Creek. The spring ceased flowing for the first time in recorded history in 2000, again ceasing to flow in 2008. This resulted in now ongoing measures to address local water conservation and quality. Hays County purchased fifty acres (202000 square meters) of land around Jacob's Well in 2010, in an attempt to protect the spring from development. An additional thirty-one acres was transferred to the county from the neighboring Jacob’s Well Natural Area (administered by the Wimberley Valley Watershed Association (WVWA)), the new, eighty-acre (323000 square meter) named the Westridge Tract. With the general decrease in water flow through the cave system, divers were for the first time able to descend directly to the first chamber.
Jacob's Well is considered a dangerous underwater cave for novice or non-cave trained SCUBA divers, with a dozen divers having died in the system. At the present, four chambers have been explored, the last of which ends in a restriction too narrow for divers to continue.