Alley Mill uses water from the spring, not the river, to operate. Big Spring: Located near Van Buren, Missouri in Ozark National Scenic Riverways' Big Spring Campground, this is the largest spring in the state, and one of the largest in the world. On an average day, some 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 coming to the surface at Big Spring. The trip took from 7 to 14 days. More on Big Spring.