Springs form where groundwater is forced up and onto the surface through openings in the ground.  This is caused by the differences in the slope or "hydraulic gradient" in the aquifer.  As rain falls and percolates underground, it exerts pressure on the water already in the aquifer, forcing some to the surface through natural openings.  As these holes gradually become bigger, water from the aquifer below bubbles up into clear, cool pools that provide homes to rare and unusual fish, amphibians, and insects. Blue holes also provide a sanctuary for a large number of animals and birds. 

The highest concentration of springs are located in north-central Florida where the aquifer is closest to the surface. Springs are classified or categorized based on the amount water discharge.  The largest springs are classified as "magnitude 1" springs which means they discharge at least 65 million gallons of water a day.  The three spring vents in Silver Springs discharge 359 million gallons of water each day\  that's the equivalent of about 7 million bathtubs full of water! (credit: http://www.floridasprings.org)

Find out more about endangered blue hole springs and the vital role they play. Visit http://www.floridasprings.org/expedition/dispatch1/