http://www.karstproductions.com/image_gallery/gallery_2.html
Inland blue holes are unlike any other environment on Earth, thanks largely to their geology and water chemistry. In these flooded caves, such as Stargate on Andros Island, the reduced tidal flow results in a sharp stratification of water chemistry. A thin lens of fresh water—supplied by rainfall—lies atop a denser layer of salt water. The freshwater lens acts as a lid, isolating the salt water from atmospheric oxygen and inhibiting bacteria from causing organic matter to decay.
"All of a sudden, it's got you," says photographer Wes Skiles of the "insanely dangerous" vortex in Chimney Blue Hole off Grand Bahama. Like a giant bathtub drain, it sucks down millions of gallons when the tide comes in. "It's like going over a waterfall—there's no escape." Wes Skileshttp://www.npr.org/templates/story/story.php?storyId=128704761&sc=fb&cc=fp
http://synaesthetical.blogspot.com/2010/07/blue-holes-of-bahamas-wes-c-skiles.html
Freshwater Lens | Judy Watson
http://uapmarker.com.au/2010/03/23/freshwater-lens-judy-watson/
Heron Island artworks ~ http://www.uq.edu.au/news/?article=19810
Judy Watson pictured with her Freshwater Lens artwork, suspended beneath the Turbot Street overpass in Brisbane.