Big Spring is a major karst spring in the Missouri Ozarks, rising from a limestone bluff along the Current River valley near Van Buren. Among the largest springs in the United States and the world, it averages 470 cubic feet of water per second and forms the second-largest tributary of the Current River. Its aqua-blue water surges from the bluff, then runs about 1,000 feet before entering the river, remaining near 58 degrees Fahrenheit. Fed by a vast underground drainage network reaching into the Eleven Point River watershed, the spring continually enlarges as groundwater dissolves limestone, making it one of the Ozarks’ defining natural features.