Around 1903, Andrew J. Zilker and the Elks Club built a concrete amphitheater around Eliza Spring for keeping cool during meetings in the summer. The amphitheater allowed for the pre-existing spring run to follow its natural course. A few decades passed and the natural spring opening was covered with concrete to form a solid base for the amphitheater. From this point on, the only inflow from the aquifer into Eliza Spring is a series of small (6-8”) upwelling holes and a series of 15 vents around the base of the lowest bench of the amphitheater. Outflow has since been altered to follow a concrete tunnel underground and to discharge into the Bypass beneath the north sidewalk at Barton Springs Pool.