Yucatan Peninsula, Mexico
While there is great potential for cave diving in the continental karst throughout Mexico, the vast majority of cave diving in Mexico occurs in the Yucatán Peninsula.
While there are thousands of deep pit cenotes throughout the Yucatán Peninsula including in the states of Yucatán and Campeche, the extensive sub-horizontal flooded cave networks for which the peninsula is known are essentially limited to a 10 km wide strip of the Caribbean coastline in the state of Quintana Roo extending south from Cancun to the area of Tulum and the Sian Ka'an Biosphere Reserve, although some short segments of underwater cave have been explored on the north-west coast (Yucatán State).
In the Yucatán Peninsula, any surface opening where groundwater can be reached is called cenote, which is a Spanish form of the Maya word d'zonot. The cave systems formed as normal caves underwater, but upper sections drained becoming air filled during past low sea levels. During this vadose, or air filled state, abundant speleothem deposits formed. The caves and the vadose speleothem were subsequently reflooded and became hydraulically reactivated as rising sea levels also raised the water table. These caves are therefore polygenetic, having experienced more than one cycle of formation below the water table. Polygenetic coastal cave systems with underwater speleothem are globally common, with notable examples being on the Balearic Islands (Mallorca, Menorca) of Spain, the islands of the Bahamas, Bermuda, Cuba, and many more.
As with all cave speleothems, the underwater speleothems in the Yucatán Peninsula are fragile. If a diver accidentally breaks off a stalactite from the ceiling or other speleothem formation, it will not reform as long as the cave is underwater so active cave conservation diving techniques are paramount.
In plan form, the Quintana Roo caves are extremely complex with anastomotic interconnected passages. When cave diving through the caves, the pathways then appear to have many offshoots and junctions, requiring careful navigation with permanent tees or the implementation of jumps in the guideline.
The beginning of the 1980s brought the first cave divers from the U.S. to the Yucatán Peninsula, Quintana Roo (Q.Roo) to explore cenotes such as Carwash, Naharon and Maya Blue, but also to central Mexico where resurgence rivers such as Rio Mante, sinkholes such as Zacaton were documented.
In the Yucatán, the 1980s ended with the discoveries of the Dos Ojos and Nohoch Nah Chich cave systems which lead into a long ongoing competition of which exploration team had the longest underwater cave system in the world at the time, with both teams vying for first place.
The beginning of the 1990s led into the discovery of underwater caves such as Aereolito on the island of Cozumel, ultimately leading to the 5th biggest underwater cave in the world.
By the mid 1990s a push into the central Yucatán Peninsula by dedicated deep cave explorers discovered a large number of deep sinkholes, or pit cenotes, such as Sabak Ha, Utzil and deep caves such as Chacdzinikche, Dzibilchaltun, Karkirixche that have been explored and mapped. To this day these deep caves of the central Yucatán remain largely unexplored due to the sheer number of cenotes found in the State of Yucatán, as well as the depth involved that can be only tackled using technical diving techniques or rebreathers. In the end of the last millennium closed circuit rebreather (CCR) cave diving techniques were employed in order to explore these deep water filled caves.
By the end of the 1990s, The Pit in the Dos Ojos cave system located 5.8 km from the Caribbean coast in the state of Quintana Roo had been discovered, and it is presently (2008) 119 m deep. At that time, technical diving and rebreather equipment and techniques became common place.
By the turn of the millennium the longest underwater cave system, called Ox Bel Ha was established by cave diving explorers whose combined efforts and information helped join segments of previously explored caves. The use of hand held GPS technology and aerial and satellite images for reconnaissance during exploration became common. New technology such as rebreathers and diver propulsion vehicles (DPVs) became available and were utilized for longer penetration dives. As of January 2008, Ox Bel Ha includes 170 km of underwater passage (See QRSS for current statistics).
Active exploration continues in the new millennium. Most cave diving exploration is now conducted on the basis of "mini projects" lasting 1 – 7 days, and occurring many times a year, and these may include daily commutes from home to jungle dive base camps located within 1 hour from road access.
In 2006 and 2007 a number of large previously explored and mapped cave systems have been connected utilizing sidemount cave diving techniques and many times no-mount cave diving techniques in order to pass through these tight cave passages, creating the second largest connected underwater cave systems on the planet, Sac Actun, which presently has a length extent of 155 km (See QRSS for current statistics).