About Cenotes of Mexico
Many of them are open to the public for swimming, diving, and exploration. Many are open, however some of them are partially underground and the caves associated with these cenotes can run for miles underground. Cenotes also vary in size with openings as little as a foot wide to as large as a small lake.
The water clarity in these cenotes is often unsurpassed, often exceeding 200 feet, and makes for exceptionally good swimming. Some of the bigger cenotes are available as tourist destinations, many are locally owned, and many more still are either undiscovered or undeveloped.
The underground river systems of the Yucatan flow beneath the entire peninsula. During the ice ages when the ocean levels were much lower than they are today, what was once a giant coral reef became exposed to the atmosphere and eventually became the Yucatan Peninsula. Massive cave systems were formed by gradual dissolving of the highly porous coral limestone.
These caves are called "solution caves" because they were formed by the slightly acidic rainfall dissolving the alkaline limestone. Inside the caves the geological formations such as stalactites and stalagmites are a spectacular sight to see. Many of the caverns eventually collapsed and the sea levels rose partially or completely flooding the cave systems.
The water table of the entire peninsula is filled with consists of seawater at sea level and freshwater 'floating' on top at varying depth depending on the distance from the sea. For instance, Cenote Zaci in Valladolid in the central Yucatan area is about 35 metres from ground level to the surface of the freshwater and probably another 30 metres below that would be the top of the saltwater layer.
It has been estimated that there are approximately 30,000 cenotes or exposed access points to these cavern and cave systems and thousands of miles of underwater cave passageways have already been explored and exploration continues in too many systems to count. Two of these cave systems have over 140 km of explored passages.
Cenotes are complexes of sinkholes and caves in the Karst geological landscape of the Yucatán. Some cenotes contain spectacular cave formations, while others are important archaeological sites, and several were considered sacred by the Mayans. A few are open to the public for swimming and diving. Of the estimated 30,000 cenotes, many of them unexplored, many are considered to be Mayan cultural and archaeological sites. Ancient fossilized remains of Camels, giant Jaguars and Mammoths are among the interesting archaeological finds in recent years. Most of these have been found by cave divers exploring underwater cave systems and some sites are now protected by INAH, the Mexican government archaeological and historical protection organisation.
Recently, experienced divers have discovered Maya artifacts upsteam of some of the sinkholes they explored dating back over 1,000 years. This has led them to conclude that the water table in this area was significantly lower at one time and the Maya inhabited the caverns which are now full of water. They also concluded that some of the sacrifices made, were to ask the spirits to lower the water table so that they could resume life in the caverns. They also believed that the Maya remained in the area for some time living above ground, while waiting on the waters to recede, before moving on.