The Outdoor Weblog

Location: Off of Coba Road outside of Tulum, Mexico

Depth: 60 feet

Advantage: A swim around the hat's brim at 60
feet is a tour of a multilevel maze of cave formations, boulders and stalactites dripping from the blanched white limestone.

Risks involved : Entry point is uncomfortable.

A cave dive here means going into Half-fresh water and half-salt water. If you also take a cavern dive, you will be able to spot many fossils in the clear water.

4. Conch Sound diving site

Location: Blue Hole cave system, Andros, Bahamas

Depth: 90 feet

Advantage: When you dive in the caves, at a depth of about 25 to 30 feet, you can see the fresh / alt water interface, or "halocline," as a distinct line separating the liquids, and if you watch a diver passing through the halocline, their image is shortly blurred and distorted by the mixing of the fresh and salt water.

Risks involved: The ocean blue holes will "blow" and "suck" making it necessary to dive them at certain times. The "blow" usually pumps out cold subterranean water which may be milky with hydrogen sulfide and algae or, during the "suck," the water will be gin clear as it sucks in the surrounding sea water. Too little light penetrates the depths for this drowned crater.

1. Aussie's Black Holes

Location: Andros, Bahamas

Depth: 2000ft

Risks involved: Black layer with zero oxygen and a very high level of hydrogen sulphide, that might be due to temperature reading, 37¡C, and the low pH reading indicating an acid environment. A total hell hole!