Hundreds of springs rise at the head of Ozark rivers. Some are so small, they are no more that a wet place, soaking the ground. Then there is Big Spring, which boils up from an underground system and draws water from a 505 square mile recharge area. It delivers 286 gallons of water a day to the Current River. Alley Spring looks so calm. But look closely: the grass anchored in its bed strains for the Jacks Fork River. Native Americans named Blue Spring, a tributary of the Current, because they thought it reflected the blue of the sky. Actually, limestone, eroded from its underground system, colors its water blue. Roaring River Spring rises from an underground cave that reaches hundreds of feet back into a massive bluff. The roof of the cave hovers low over a blue pool. A small spring that pours over the bluff eroded a tall niche in the bluff and rains down on the spring rise at its base.