Source: https://www.freedomsphoenix.com/News/072452-2010-07-21-bahamas-reporting-big-blue-holes-under-water.htm

Source: http://howtospendit.ft.com/adventure/37463-cave-diving-in-mexico

Photograph by Agnes Milowka, Wes/Karst Productions

Photograph by Wes C. Skiles

Source: http://www.thebahamasweekly.com/publish/local/Islands_of_Bahamas_Blue_Holes_to_be_featured_on_JCN17441.shtml

Source: http://howtospendit.ft.com/adventure/37463-cave-diving-in-mexico

Source: http://amazingezone.com/interesting/great-blue-hole-of-belize/