Alapaha Rise, also called Shelley Run, is a major spring in Hamilton County, Florida, near where the Alapaha River approaches the Suwannee River. Classified as a First Magnitude spring, it is identified as the largest single spring in the United States. Its average flow is about 802 cubic feet per second, and its water enters the Suwannee River about one-third of a mile upstream from the point where the Alapaha joins it. Unlike the clear blue water often associated with Florida springs, Alapaha Rise has high tannin levels that give the water a darker appearance.