Category Archives: Cave Diving

Cave diving is one of the most challenging diving activity and requires a variety of specialized procedures.

The activity originated in the UK with the need for cavers to dive sump to continue their dry cave exploration.

Underwater caves have a wide range of physical features, and can contain fauna often endemic.

Sac Actun System – The longest cave system in the world

Sac Actun System is now officially the longest flooded cave system in the world
Sac Actun system
Cavern at Cenote Pet Cemetery

– With a total length of 347 kilometers, (216 miles) Sac Actun is the largest flooded cave in the world
– It is the result of many hours of exploration and hard work leading to the connection of Sac Actun System 263 kilometers (161 mi) and Dos Ojos 84 kilometres (52 miles).

Cave exploration background

On January 10th, 2018, the Underwater Exploration “Group Gran Aquifero Maya” (GAM), succeeded in connecting  two of the largest flooded cave systems making it the longest flooded cave in the world.

While Robbie has been actively looking for this connection during the last 14 years and adding new tunnels and galleries to this underwater maze, this stage of the project started in March 2017.

Until then, the 4 largest cave systems ranked as follow:

  1. Ox Bel Ha System – 270 kilometers/ 163 miles
  2. Sac Actun System – 263 km/161 miles
  3. KooX Baal System – 93 km/57 Miles
  4. Dos Ojos System – 84 km/52 Miles
The Sac Actun – Dos Ojos Connection

Sac Actun SystemSac Actun and Dos Ojos are now connected as a result of this intensive exploration.

According to the rules of caving, when two cave systems are connected, the largest cave system gives its name to the new one. Therefore the name of the Dos Ojos system disappears :'( .

Hence, the Sac Actun System is now the largest system in the world, with a length of 347 kilometers – 215 miles of flooded cave.

This finding is also very valuable, because this system supports a great biodiversity that live thanks to this huge reserve of fresh water.

Future projects

But of course, underwater cave exploration is far from finished! New objectives pop up and the goal is now to connect Sac Actun with other nearby underwater cave systems in the municipality of Tulum.

Local explorers seek to better understand the underground of the Yucatan peninsula. And, they also investigate its biodiversity and the relationship of the humans with these ancestral waters. Of course, very concerned by their environment and pasionate, the aim is to manage an adequate use of the natural resources from this aquifer.

There will be more very ambitious stages to this project. Among those, stands the analysis of the water quality of Sac Actun System. As well, there will be studies of the biodiversity and its conservation; in addition to following up the mapping and investigating the submerged archaeological sites.

According to the Quintana Roo Speleological Survey (QRSS), the north of Quintana Roo alone hosts 358 submerged cave systems. It represents around 1400 km – 870 miles of flooded caves.

The word of the restless explorer, Robert Schmittner

“This is an effort of more than 20 years, to travel hundreds of kilometers of caves submerged in Quintana Roo mainly, of which I had dedicated 14 years to explore this monstrous Sac Actun System; now everyone’s job is to conserve it”

Robert Schmittner.

The word of the National Institute of Anthropology and History (INAH) and Director of the GAM Project, Guillermo de Anda

“This immense cave represents the most important submerged archaeological site in the world, as it has more than a hundred archaeological contexts. Along this system, we had documented evidence of the first settlers of America, as well as extinct fauna and, of course, the Mayan culture.”

Tulum: the mecca of cave diving.

Underwater explorers from all over the world have devoted their lives to their passion for exploration. Among them Bil Phillips, pioneer of the exploration of the Mayan aquifer. He founded together with James Coke, the Quintana Roo Speleological Survey (QRSS). The QRSS database gathers detailed maps of these complex systems. Today it is a valuable tool to understand and protect the aquifer.

Dedication to Bil Philips

Bil Phillips explored this wonderful underwater world until the last days of his life. For more than 40 years he devoted himself to understand the aquifer through the investigation of these ancestral waters.

Bil Phillips was an underwater cartographer and explorer, he passed away in November 2017.

Who can dive Sac Actun?

All certified cave divers can discover the Sac Actun System. Obviously with 347 km it leaves the possibility of many hours of diving. The system also has many entries. Do not hesitate to contact us to guide you in the most beautiful tunnels of the network.

For recreational divers interested in discovering these underwater cave network we offer cave diving training.


Playing with the Halocline

A cave dive playing in the halocline, meeting with remipedes

This cave is just amazing, dark with a very well defined halocline. Recommended to dive with Nitrox and with stage side mount or stage back mount configuration as it is fairly deep and you will want to stay as long as posible.

Halocline: from Greek hals, halo- ‘salt’ and klinein ‘to slope’

The halocline is the area within a body of water that marks a drastic change in salinity.

Haloclines are common in underwater caves near the ocean. The fresh water, less dense, forms a layer above the salt water from the ocean. For cave divers, it causes the optical illusion of air space in caverns. Passing through stirs up the layers and blurs the vision.

The halocline itself is responsible for the formation of the cave systems. The mixing of the saltwater and freshwater results in reactive brackish water that dissolves the limestone, eroding the rock and enlarging a cave’s passageways.

Because different water densities meet at the halocline and both organic and inorganic particulates accumulate there, it is chemically speaking an intriguing place.


Contact us for private guided dive in hidden side passages.


Guided dives

Bull Sharks - Playa del carmen

Guided Dives on the second largest reef in the world – Experience the thrill of diving with bull sharks – Day trips to cozumel from Playa del Carmen – Express trips to Cozumel.
We also offer technical ocean diving


Unique in the world: discover cavern diving in the Cenotes – Dive Cenotes near Tulum and near Playa del Carmen – Cenotes in Puerto Morelos for Advanced divers – Special private and personnalized trips to the Cenotes of Yucatan


The best way to discover the amazing caves of Yucatan – We offer all level of cave diving from beginners to more advanced –
Stage cave diving – DPV Cave diving – CCR cave diving – Trimix CCR

Treat yourself with a tailor made diving holliday in the Cenotes, ask us and we make it happen! 

Cave diving – Line protocols

Line protocols in cave diving


line protocols
Full cave diving course – Use of directional and non directional markers

Guidelines are the life lines used by cave divers to reference the exit in underwater caves. In case of loss of visibility the guideline will lead to the way out of the cave, back to the surface and to ambient air. One of the main reason for fatalities in cave diving involves the lack of use of a continuous guideline. It can be either for not running a temporary line from the open water to the permanent guideline or for passing from one line to another.

For maximum safety, cave divers follow a continous guideline  that can lead them all the way to the surface, even in total darkness. Directional markers such as arrows and personal non-directional markers such as “cookies” or REMs on the lines clearly indicate the exit.

Permanent Lines

Permanent lines are installed permanently in the cave to insure a properly installed guideline for further going exploration and visiting cave divers.

The permanent lines are often referred to as main line. They can begin close to the cave exit or further into the cave hidden from open water divers and prevent them to go into the cave without proper training. Divers travel to the mainline with a primary reel in order to keep a continuous guideline from the open water.

Navigation in Caves

In most caves, especially in the Yucatan peninsula in Mexico, there are more than one permanent line therefore the divers have to navigate inside the cave. There are permanent intersections, referred to as a “T“.

Sometimes a diver has to phisically move from one line to another this is a jump. It can go from the end of one line to the middle of another, or from the middle of a line to the end or middle of another.

A gap is when going from the end of one line to the end of another.

Personal line markers properly mark the exit. It has to be in a clear way in order to be understood in zero visibility. The diver will be able to find the way to the open water area of the cave entrance.

Gap and/or Jump Lines

Divers have to install a temporary gap or jump line to go from one line to the other. Line markers such as directional or non-directional should also indicate and mark the exit.

Laying line

Proper use of reels and placement of lines is essential for efficient cave diving. The line has to be laid maintaining tension. It should be placed close to the cave floor so divers can swim above it.
A primary tie off should be made in open water where direct ascent to the surface is possible. It is followed by a secondary tie off in the cavern zone. Should the primary tie off come loose the second one will keep the line in place. Further on a tie-off or placement must be made whenever changing direction in order to avoid line traps.

Line Markers

Line markers indicate directions or mark survey or science stations. They can be directional (arrows) or non-directional markers (cookies, clothespins, REM). Personnal non-directional markers are mark locations or exits and will not cause confusion for other teams.

You will learn more about the use of guidelines and line markers and practice their uses in real caves and various scenarios during your cave diving training.



Plongée dans le Yucatan, Mexique  –  Cours de plongée et Plongées guidées

Deep Dark Diving offre un service personnalisé pour vos plongées dans la Riviera Maya et le Yucatan au Mexique

Dévoués à la sécurité et à la conservation, nous sommes spécialisés dans la plongée Cenote et la plongée souterraine. Nous offrons des plongées guidées ainsi que des formations en plongée souterraine et plongée technique pour plongeurs débutants et confirmés.

Nous avons une passion pour la plongée, une passion pour les grottes, une passion pour la plongée souterraine que nous aimons partager avec vous afin de vous faire profiter au mieux de votre expérience de plongée sous-marine dans le Yucatan.


Bull Sharks - Playa del carmen


Récifs de Playa del Carmen - Akumal - Plongée a Cozumel depuis Playa del Carmen - Requins bouledogues


Unique au monde: découvrez la plongée en caverne dans les Cenotes


Découvrez le monde caché des Cenotes du Yucatan – Stage – DPV – CCR


Cenote Kukulkan, plongée caverne dans la lumière hivernale


Premier pas vers la plongée souterraine. Vous apprendrez les procédures de la plongée sous plafond dans la zone de lumière naturelle

Introduction à la Plongée souterraine


Voilà! C’est parti dans l’obscurité totale et vous pourrez réaliser des plongées simples au-dela de la zone de lumière naturelle

Cours de plongée souterraine


Les réseaux souterrains peuvent être très complexes, surtout au Mexique. Vous pourrez maintenant combiner tout ce que vous avez appris avec des navigations complexes et plus encore


Introduction à la plongée technique


Bases de la plongée technique – Plannification – nouvelle configuration et meilleur hydrodynamisme – Améliorer flottabilité et techniques de palmage. Etablir une base solide. 

Cours de plongée Sidemount


Premiers pas en configuration Sidemount. Pour plongeurs tec souhaitant transposer leurs aptitudes à la configuration Sidemount. Ou pour débutants ayant choisi la configuration Sidemount.


Un cours de Side Mount plus approfondi. Il couvre les bases necessaires à la plongée technique et la plongée souterraine et constitue une base solide. De plus votre harnais Razor vous suivra à tous les niveaux de plongée technique.


Nitrox sticker SDI TDI - TDI Nitrox Course


Premier pas vers l’utilisation de mélanges. Pour plongeur Nitrox certifié c’est l’occasion de revoir les bases théoriques, la physique et les lois fondamentales en profondeur avant d’aller plus loin.

Cours de Nitrox Avancé


Physique et physiologie de la plongée aux mélanges contenant plus de 40 % d’oxygène. Rallonger votre temps de plongée sans entrer en décompression

Cours de procédures de d´compression


Plannifier et réaliser des plongées a décompression . Choix des gas et exécution de plan d’urgence.


Deco stop at Cenote the Pit, Dos Ojos


Des plongées superbes à  55m/180ft mais pas d’helium disponible? Vous apprendrez comment plonger en sécurité en utilisant de l’air et des gaz de décompression.

Cours de plongée trimix


Rajoutez l’hélium à vos plongées. Allez plus profond, respirez mieux et réduisez la narcose. Ca rend vos plongées beaucoup sûres et offre de nombreuses possibilités jusqu’à 60m/200ft.

Cours de trimix avancé


Félicitations! Vous avez atteint le plus haut niveau de plongée en circuit ouvert. Utilisez des mélanges avec moins de 17% O2 et à des profondeurs de 100m/330ft. Et faites partie de l’élite de la plongée.

Dive Razor Original
ISC Megalodon



 Scuba Diving in Yucatan
Dive Training and Guiding

Deep Dark Diving provides personalized service for your diving in Yucatan, Mexico. Private guiding for individuals and special packages for groups.

Highly committed to safety and conservation we specialize in Cenote cavern, cave and Tech diving. We offer guiding and training for recreationnal divers and for advanced technical and cave divers.

We have a passion for diving, a passion for caves, a passion for cave diving and we’d love to share it with you and make sure you get the most out of your scuba diving experience.

Diving yucatan
Beautiful Cenotes of Yucatan


Bull sharks diving - Mexico


Dive the second largest reef in the world – Experience the thrill of diving with bull sharks

Cavern diving in the Cenotes


Unique in the world: discover cavern diving in the Cenotes



The best way to discover the amazing caves of Yucatan –
Stage – DPV – CCR


cavern diver course


First step in the Overhead environment. You will learn all safety protocols within the daylight zone. 

Intro to cave diver course


That’s it! this is the first step in the dark caves. You will learn how to do simple cave dives beyond daylight zone

full cave diving training


Caves can be complex, especially in Mexico, you will now combine previously learned skills with complex navigation, and more.


Intro to Tech Diving training


Basics for tech diving in Backmount configuration: dive planning, water skills, gear configuration, streamlining, buoyancy and propulsion techniques

Side Mount Diving Training


Get familiar with the side mount for Tec divers wanting to learn the configuration or recreational divers taking their first steps into the Tec or cave diving world

Razor Side Mount Diving Course


The Razor Side Mount course covers the basics for tech and cave diving further than basic courses. Then you can focus on the core of subsequent training in your Razor.



TDI Nitrox Course


A first approach to technical diving and the use of mixtures. And for those already Nitrox certified diver it is the opportunity to thoroughly review the basic principles and fundamental laws of physics used in diving.



You will learn the physics and physiology for diving with gas mixtures containing more than 40 % oxygen. This is the opportunity to further extend of your dive time without going into decompression limits.



In this course you will learn to plan and execute dives with decompression, choose your gas and the development of emergency plans.


Extended range course


Exciting dives down to 55m/180ft but helium is nowhere available? you will learn how to safely do these dives using air and deco gases.



Add helium to your diving. Go deeper, easier breathing, and reduce narcosis. It makes your diving a lot safer and opens a lot of possibilities down to 60m/200ft.

Technical diving training - Advanced Trimix diving


Congratulations! you reached the top level of Open circuit training. Use mix with less than 17% O2 and as deep as 100m/330ft. And be among the most elite divers.

Dive Razor Original

About the Cenotes


The word “Cenote”, comes from the mayan “D’zonot” and means “well”.

Cenotes are natural pits, or sinkholes, resulting from the collapse of limestone bedrock therefore exposing the ground water underneath. Cenotes are common geological forms in low latitude regions, particularly on islands, coastlines, and platforms with young limestones with little soil development. They spread all over the Yucatán Peninsula of Mexico. The term “cenote” also describes similar karst features in other countries such as Cuba and Australia, in addition to the word “sinkholes”.

Diving into the cenotes is like diving into the history of the peninsula of Yucatan and much more. It gives a wonderful chance to appreciate the evidence of geological changes, archeological discoveries, extinguished species fossils…

The best way to discover the Cenotes will be by cavern diving or cave diving, getting cave diving training.



Cenotes are the connections to the subterranean water bodies. They can feature large open water pools or small sheltered pools. Sometimes they do not have any exposed water. There are over 6000 different cenotes in the Yucatan Peninsula in Mexico.

Cenote waters are usually crystal clear, as the water comes from rain water filtering slowly through the limestone. Therefore contains very few particules. For cave divers great pleasure, cenotes sometimes reveal an underlying cave system.

The Yucatan Peninsula is now officially host of the longest cave system in the world, s system Sac Actun with 347 km. Thanks to  many years of hard work and many hours of exploration, active explorers recently connected  Sac actun (264 km) and Dos Ojos (83km) underwater (January 2018).

Cenotes around the world attract cavern and cave divers.

The Yucatán peninsula

CenotesFormed during the Cenozonic era, – 65,000,000 years ago, the peninsula of Yucatan is very young. The entire peninsula was once a reef, but as the water level dropped, the flatland of Yucatan emmerged.

The peninsula is the exposed portion of the larger Yucatán Platform composed mostly of limestone . The whole of the Yucatán Peninsula is an unconfined flat lying karst landscape.

65 million years ago a meteorite impacted in the greater Caribbean Basin. The center of Chicxulub crater is deeply buried  off the north coast of the peninsula near the town of Chicxulub. The famous “Ring of Cenotes”  outlines one of the shock-waves from this impact, which lies more than 1 km below the modern ground surface.

Although cenotes spread widely throughout much of the Yucatán Peninsula, a higher-density circular alignment of cenotes overlies the ridge of the Chicxulub Crater. This crater structure, identified from the alignment of cenotes, along with geophysical methods.


Cenotes - Karst of MexicoLimestone is a sedimentary rock composed primarily of calcium carbonate (CaCO3) in the form of the mineral calcite. It mostly forms in clear, warm, shallow marine waters. It is an organic sedimentary rock that forms from the accumulation of shell, coral, algal and fecal debris. It can also be a chemical sedimentary rock formed by the precipitation of calcium carbonate from lake or ocean water.

Dissolution of the limestone, formation of the caves

For the Chemists this is how it goes:

Cenotes Limestone dissolution – Chemical reactions leading to cave formation

Gunn J. (Ed.) 2003. Encyclopedia of Caves and Karst Science. Routledge. New York

Calcium precipitation in the Cenotes forms a white layer at the surface

Flora and fauna

Flora and fauna are generally more limitted than in the open ocean, however marine animals do prosper in caves. In caverns, one can spot mollis, guppies, cat-fish, small eels and turttles. In the darkest cenotes, the fauna has evolved special features to live in an the absence natural light. For example, most cave fauna doesn’t have pigmentation and is often blind. They are equipped with sensors in order to find food and make their way around in the dark.

Remipede (Speleonectes tulumensis)

Remipedes are primitive centipede-like crustacean. They can grow up to an inch (2.5 cm) and they use venomous fangs to capture their prey. No other crustacean has this characteristic.

Isopod (Metacirolana mayana)

These cave scavengers feed on whatever comes accross their claws (usually smaller crustaceans).

Mexican Blind Fish (Typhliasina pearsei)

A fish species that inhabits the brackish and freshwater layers of the Yucatan’s caves. The albino, sightless fish grows a couple inches (5 cm). And unlike most other fish, it gives birth to live young.


Side mount cave diving in cenote Minotauro

A day off, cave diving

A cave dive at Cenote Minotauro.

Cenote Minotauro is an easy place to reach. You arrive on a parking lot with tables (at the right height)! And new bathrooms 🙂

The access to cenote Minotauro is through a nice stairway and you can just walk into the water.

I have dove a lot in this system in Backmount configuration, however, it is really nice for side mounting and gives access to many more passages. In Side Mount configuration it is much more enjoyable and probably more precise and easier to avoid damage on the cave.  This system goes up and down, reaches the halocline but remains fairly shallow and is a great place for long dives.

The system itself and the dive circuits can seem a bit confusing as you start knowing the system but it is all really pretty. There is a great map of Minotauro by Alessandro Reato, that really gives all its sense to following Ariadne’s line as this place is really a labyrinth.

You will see here a few images of a fun dive with a friend, local instructor. This video has no teaching purpose whatsoever. No pretension, just two local instructors and experienced cave divers enjoying their time cave diving, filming, editing and sharing their passion.

When this dive was finished, as the current had pushed us quite fast towards the exit we still had plenty of air to recalculate thirds and have a short dive on the other side, downstream so beautiful again. But guess what, the camera’s battery was dead!! I guess we’ll have to go again.

See you,



Anchialine caves and their fauna

Great ressources for all passionate cave divers who can never learn enough about cave geology and cave fauna:

You can learn about the caves in Yucatan, the caves in the bahamas and the caves in Bermuda, their geology and their fauna.

Although not up to date it is still great information.

Watch our videos to observe some of the amazing fauna that you may encounter while cave diving in the Yucatan peninsula in Mexico.

Let us guide you into those amazing dives and observe blind fish, remipedes and many more in their natural habitat. (More info about cave diving)