There are no rivers in the Yucatan peninsula, only sinkholes and underground caverns full of water. My dive buddy, Roger, and I decided to take the ferryboat from Cozumel to Playa Del Carmen for a day of Cavern diving in the cenotes of Quantana Roo, Mexico. We were guests for the day of the DeRosa family. They are well known for their early explorations of the areas sinkholes. Our French guide, Herve, a very accomplished cave & cavern diver, pointed out many fossils and some ancient pottery left by early dwellers who lived in the caves before they subsided below sea level. 

There are no fish or other life forms to be seen within the caverns themselves. Only at the sunlit entrances could we see small fish and other creatures dwelling. The water was crystal clear. It gave me the feeling of floating weightlessly through nothing. I had to fight the impulse to remove my mask and regulator while examining, close up, the many wall and ceiling structures. Sharp columns of sunlight punctuated the many dark caverns. 

A most interesting phenomenon occurs where ocean water meets fresh water. This horizontal layer, called the holocline, is similar to the vinegar/water interface we are all familiar with, salt water on top and fresh water below. This thin layer is fuzzy enough to cloud your vision as you pass through it. And if you are immediately beyond another diver the layer become turbid and expands to several feet in thickness.