The increase in the number of visitors during the past several years at Mammoth Cave National Park has rendered the present water supply inadequate. Emergency measures were necessary during August 1962 to supplement the available supply. The Green River is the largest potential source of water supply for Mammoth Cave. The 30-year minimum daily discharge is 40 mgd (million gallons per day) . The chemical quality is now good, but in the past the river has been contaminated by oil-field-brine wastes. By mixing it with water from the existing supply, Green River water could be diluted to provide water of satisfactory quality in the event of future brine pollution. The Nolin River is the next largest potential source of water (minimum releases from Nolin Reservoir, 97-129 mgd). The quality is satisfactory, but use of this source would require a 8-mile pipeline. The present water supply comes from springs draining a perched aquifer in the Haney Limestone Member of the Golconda Formation on Flint Ridge. Chemical quality is excellent but the minimum observed flow of all the springs on Flint Ridge plus Bransford well was only 121,700 gpd (gallons per day). This supply is adequate for present needs but not for future requirements; it could be augmented with water from the Green River. Wet Prong Buffalo Creek is the best of several small-stream supplies in the vicinity of Mammoth Cave. Minimum flow of the creek is probably about 300,000 gpd and the quality is good. The supply is about 5 miles from Mammoth Cave. This supply also may be utilized for a future separate development in the northern part of the park. The maximum recorded yield of wells drilled into the basal ground water in the Ste. Genevieve and St. Louis Limestone is 36 gpm (gallons per minute). Larger supplies may be developed if a large underground stream is struck. Quality can be expected to be good unless the well is drilled too far below the basal water table and intercepts poorer quality water at a lower level. This source of supply might be used to augment the present supply, but locating the trunk conduits might be difficult. Water in alluvium adjacent to the Green River and perched water in the Big Clifty Sandstone Member of the Golconda Formation and Girkin Formation have little potential as a water supply.