Florida has over 600 springs producing more than 8 billion gallons of water a day, including thirty-three First Magnitude springs, each flowing at more than 65 million gallons per day, the largest concentration of freshwater springs on earth. Their abundance comes from karst terrain, formed as rainwater enters the ground and dissolves limestone bedrock, creating sinkholes, caverns, and springs. The underground river in this porous limestone, called the Florida Aquifer, supplies 90% of the state's drinking water, and springs are windows on that aquifer, showing the water after it has traveled through the ground beneath towns, farms, businesses, and lawns. Silver Springs is probably the largest First Magnitude spring in the United States and one of the world's largest, with an average daily flow of more than 500 million gallons. It consists of 30 springs with 61 vents, including Mammoth or Main Spring, whose vent measures 5 feet by 135 feet at a depth of 30 feet. Its water remains 72 degrees year-round, is about 20 years old from the time it fell as rain, forms the Silver River, and flows 4 1/2 miles to the Ocklawaha River. Silver Springs has attracted people for over 12,000 years and was designated a National Natural Landmark by the U.S. Department of the Interior in 1972.
