Blue Spring is located approximately 12 miles east of Eminence on Highway 106. The spring flows slowly from a very deep cave shaft that is situated at the base of a dolomite bluff. It is is the largest spring in Missouri and the largest freshwater spring in the United States. On an average day, around 278 million gallons of water gush forth from subterranean passages, swelling the nearby Current River. Experiments in which harmless dye is placed into the ground have shown that water travels from as far as 45 miles away through underground passages before surfacing at Big Spring.