Depth and DCI: What Happened At The CMAS 2025 World Championship
At the recent CMAS 2025 Freediving Depth World Championship in Mytikas, Greece, a serious incident involving Russian athlete Andrey Matveenko, caused the focus of the event to be shifted from athletic performance to a critical conversation about diver safety. As athletes withdrew and others announced shallower dives, social media became a hub for speculation, worry, and accusations against CMAS. We are going to explore the chain of events leading up to and surrounding the incident, present the official accounts from CMAS and event organizers, and address the pressing questions on the mind of the freediving community regarding competition safety.
What happened to Andrey?
During an official competition training session on the 6th September, Russian Athlete Andrey Matveenko performed a dive to 126m. According to this blog post, CMAS said that âThis declaration was consistent with his known previous performances outside the official programâ and so âthere was no reason to restrict his official declarationâ.
The planned depth and dive time was going according to plan, until Andrey experienced a loss of consciousness on his ascent at around 15m. The safety team performed an underwater rescue and escorted him to the surface.
Following a rescue breath, it appears that Andrey regained consciousness fairly quickly on the surface, and CMAS told us that three safety divers then began escorting him towards the medical boat.
CMAS also said that: âitâs important to note that the safety divers were not wearing their official safety rash guards. This detail may have led some observers to mistake them for athletesâ.
As Andrey appeared to have recovered already, giving an OK sign to the team, only one safety diver remained with him to finish escorting him to the medical boat, while the other two returned to the diving line. Unfortunately, Andrey then started to express alarming symptoms of DCI: Decompression Illness (a blanket term which covers any injury from gas bubbles caused by pressure changes) including paralysis of his right side. It is unclear whether this was specifically DCS: Decompression sickness (gas bubbles forming in the tissue), or [C]AGE: [Cerebral] Arterial Gas Embolism (gas bubbles that enter the arterial bloodstream [and make their way to the brain]), however treatment is the same for both. This also included his head dropping and his eyes rolling back.
It appears that Andrey then lost consciousness again, and an athlete/doctor on scene jumped from the athleteâs boat to help get him onto the first aid platform. From here CMAS told us that âdoctor intervention took placeâ, that âall appropriate medical measures were applied, including oxygen administrationâ.
Photo courtesy of CMAS
They continued to tell us: âIt must be emphasised that two serious incidents occurred in immediate succession: in the case of Davide Carrera, a suspected DCS episode; and in the case of Andrey Matveenko, a deep blackout with pulmonary edema and suspected DCS. The doctors carried out a double evacuation in the shortest possible time, loading both athletes onto the boat. There was a delay of approximately two to three minutes in the evacuation protocol, but this did not affect the athletesâ recovery outcomesâ.
CMAS said in their statement: âAndrey was transferred by ambulance to Lefkada public hospital, then to the emergency neurological clinic of Thriassio public hospital in Athens, before being admitted to the naval military hospital where he remains hospitalized and under treatment. He is currently receiving treatment in a hyperbaric chamber and is monitored by the neurological clinicâ.
There have been online claims that the competition doctor on the scene initially objected to Andreyâs need for a chamber. Responding to this, CMAS have stated: âDr. Chatzigeorgiou never expressed any objection to Mr. Matvenkoâs admission to the hyperbaric chamber, as this decision was not within his responsibility. This was also confirmed during the athletesâ meeting (with around 40 athletes and coaches), when it was explained that certain comments made were unfounded and intended to cast doubt on the doctorâs conductâ.
Despite Andrey not being a DAN member, DAN was contacted regarding this case and offered free medical advice and guidance, both through the international medical hotline doctors and our Greek medical officer. DAN was not contacted about or involved in any other cases from the CMAS World Championship 2025.
Photo courtesy of CMAS
A delay in treatment
It has been said that Andrey was not given any treatment within a hyperbaric chamber until the early hours of the following day, with a delay between the first and following treatments, too. The incident occurred around 11:20am on the 6th September, CMAS reports that the first treatment was at 02:30am on the 7th, and the second at 00:30 on the 8th, with more regular treatment ongoing from there.
But is this the fault of CMAS? The event organisers? Or is it Greek medical procedures regarding Taravana (DCI in freediving)? Well, this is whatâs up for discussionâŚ
There are arguments that the event organisers (Diving Greece Organising Committee) were not prepared enough for serious injuries occurring, including claims that more specialised equipment should have been onhand. Others have suggested more communication between the organisers and the nearest hyperbaric chamber may have sped up Andreyâs treatment. However, the Diving Greece Organising Committee has denied this, telling us: âLocal hospitals and the hyperbaric chamber in Athens were informed in advance about the start of the competition and were on alert that freediving athletes with possible related medical issues might need to be transported to them during the event. All of the above was of course done weeks before and was writtenâ, CMAS confirmed this saying: âEmails from the organisers confirm these communicationsâ. They also had a detailed plan in place that would transfer a diver with DCI symptoms to a chamber within an estimated four hours, or quicker with a helicopter.
So if the chamber was aware of the competition happening and the potential injuries that could occur, why was it all so delayed?
It seems that although medical procedures in Greece work efficiently for scuba divers who experience DCI, there can be delays when it comes to freedivers with the same symptoms. Perhaps this is because they just donât see it as often, and as there are nowhere near as many documented cases. We spoke to Dr Evangelos Papoutsidakis who was the hyperbaric doctor advising on the situation over the phone via DAN, who told us that there was: âtoo much of a delayâ, and that the problem is âmany doctors donât understand freediving physiologyâ. He concluded by saying that âfreedivers need more protocols in placeâ and if the World Championship is to happen again in Greece there needs to be âmore communication with the naval hospital firstâ.
Due to the lack of research and -outside of the freediving community- general knowledge surrounding Taravana-specific symptoms and treatment, it might be understandable that a medical doctor weighing up the situation, who has little personal knowledge of apnea, might hesitate to put a person into a hyperbaric chamber, if that person is displaying similar signs and symptoms similar to that of other non-diving related illnesses. Afterall, that doctor holds the responsibility if something goes wrong or the incorrect treatment is given. The fact is, the literature just isnât there yet to help aid that decision. However, there have been cases with much quicker hyperbaric treatment in other areas of the world. So, we are left with the question, is Greece the best option for future World Championships?
In Water Recompression and its risks
Concerned freedivers online have suggested that when athlete Davide Carrera experienced symptoms of DCI on the same day as Andreyâs incident, and CMAS Chief Of Safety Roberto Butera did a couple of days later too, they both performed IWR: In Water Recompression (going to depth for an extended period of time to breathe oxygen and recompress following DCI symptoms). Some wondered why this wasnât offered to Andrey, too.
Athlete Talya Davidoff echoed this in her Instagram video explaining why she had dropped out from the competition, saying that both lines that had oxygen attached at 5m deep (a standard set up at competitions to allow for divers to breathe oxygen as a prophylactic to potentially reduce the likelihood of DCI symptoms after a deep dive) were occupied by other divers. She said: âno oxygen available for Andreyâ. Andreyâs coach Tatiana who was in the water with Andrey during the incident also reportedly asked for Andrey to be placed on the underwater O2 station, however, CMAS says Andrey was already unconscious again at this point.
Photo courtesy of CMAS
In response to all this CMAS told us: âThe safety protocol prescribes that, in the event of a blackout or suspected squeeze, the athlete must be assessed by the medical staff before being authorized to start the deco-oxygen procedure. Because of this, itâs impossible to know in advance when the lines will be available, not because blackout divers must first see a doctor, but because, under the current protocol, the deco-Oâ station isnât an emergency resource. Itâs meant as a preventive measure. Some athletes choose to relax for 20 minutes and swim around after their dives before using the deco-Oâ station, while some deep divers decide not to use it at all. For this reason, predicting its availability is not possible. However, in the case of Matvenko, he was not capable of performing the five-meter, five-minute protocol, nor of expressing the will to do so, due to his medical state at that time. And Andrey could not have been forced into a practice to which he had not previously agreed at the time of signing up for the competition. This procedure was never presented as an option when athletes registered, so we could not take responsibility for bringing someone underwater with oxygen against their will. This medical practice does not yet have sufficient scientific evidence, it is not officially approved, and it is not part of the protocol; therefore, we cannot assume responsibility for applying it. If Andre had been fit and had personally asked to go underwater to five meters to carry out the deco-oxygen procedure himself, we would have allowed it. However, such a request was never made by him, it came only from his coach, Tatiana, when Andre was already unconsciousâ.
They added: âMr. Butera consciously and independently decided to act outside the official competition protocol and assumed all related risks regarding his health and organisational responsibility. The same applied to Davide Carrera, who extended his decompression stop beyond the limits set by the protocol. These were personal decisions, not acts of favouritism, and Andrei Matvenko, in contrast, was not in a position to make such a decision and could not be compelled to follow a protocol outside the competitionâs official frameworkâ.
A good point about autonomy and IWR is made here. IWR has been practiced a lot in scuba and tech diving scenarios, but not in freediving. DCI in freediving is known as Taravana Syndrome by the medical community: âCharacterized by the onset of neurological symptoms after deep or repeated dives. The main clinical manifestations are cerebral, including stroke and cognitive impairment. The pathophysiology of Taravana syndrome is still widely debated, but the most accepted theory is that it is a specific form of decompression sicknessâ (Druelle et al., 2024).
Although signs and symptoms are very similar, nowhere near as much research has been done on Taravana syndrome as it has for scuba-related DCI. This is why it has not become a standardised practice within freediving yet; the information we have is based on off-the-record cases of freedivers trying it out for themselves, with no official guidelines to follow. Despite many claiming it to be very effective, it is not officially recommended by any medical practitioners or agencies (including CMAS) due to its potential risks and the lack of research so far. It is not a practice to be taken lightly.
Emergency Medicine physician and Marine Medicine Specialist, Dr Fernando âBizoâ Silva, an athlete competing at the World Championships this year wrote an open letter to the athletes and event organisers shortly after Andreyâs incident regarding CAGE in a competition setting. His thoughts included: âI wholeheartedly thank them (the organisers) with the full awareness they are doing their absolute best, between a rock and a hard place: the firm limitations imposed by the law (including Greek law, medical ethics code and CMAS regulations) and the pressure of the freediving community, which has the loudness provided by experience, but is unlimited by the law and not even by the support of scientific evidence. Donât get me wrong, if CAGE happens to me please send me underwater immediately (thatâs the freediver speaking), but Iâm fully aware that there is not enough scientific evidence to support it and you will be bound by the law (thatâs the doctor speaking)â.
Photo courtesy of CMAS
The future of CMAS World Championships
With athletes pulling back at competition this year, will they feel comfortable signing up next year? And if they do, what improvements can be made for them to feel safe?
In a video posted on apneapassion_freediving_magâs Instagram page, top athletes Davide Carrera and Alexey Molchanov discuss their thoughts on the matter. Alexey stated: âThis event should need to do better / procedures, so we donât see these accidents anymoreâ,
Davide continued: âI see things are moving, because CMAS are really open to improve everything so this is goodâ.
He concluded with: âThe depths are growing very fast, and the safety has to grow as wellâ.
When asked in the comments about what Davide would like to see improved on for future CMAS competitions, he replied: âWhat should have been done is to have a hyperbaric chamber on the diving spot, a hyperbaric doctor, and a safety team trained to act in case of DCI)â.
Others online have echoed this idea, so we reached out to CMAS for their take on the idea, they replied: âCMAS is evaluating portable hyperbaric chambers as a potential solution, but further study is required to determine feasibility according to event logisticsâ.
Dr Fernando âBizoâ Silva added in his open letter: âWe are at reaching depths and performance expectations today in our beautiful sport that have complications that CANNOT be seen lightlyâ.
He continued: âAt this point we are supposed to have some extent of intensive care capabilities ON THE BOAT, including ER/ICU/dive doctors, hyperbaric chamber, sedation and mechanical ventilation capabilities. We are not dealing with âfainting spellsâ anymore. We are dealing with full blown STROKES, not to mention the always understated and hidden pulmonary barotrauma / Every SECOND counts when itâs brain tissue dyingâ.
CMAS have expressed a desire to keep improving on the safety of competitions in future: âAs our sport develops and divers reach depths once considered impossible, the responsibility to guide this progression safely and ethically has never been greaterâ.
Photo courtesy of CMAS
Continuing: âThe CMAS Medical and Scientific Committee for freediving, under the leadership of its new director, Mr. Radoslaw Gaca, invites researchers, doctors, and athletes worldwide to pool their knowledge and experience. Together, we can achieve what has long been lacking: the recognition and implementation of international medical protocols for freediving within the global medical community.â
CMAS concluded with some reassuring words for athletes in regards to future World Championships: âCMAS is working with hyperbaric physicians and experts to enhance procedures. Research on IWR continues; CMAS does not exclude its possible introduction once adequate safeguards are in place. World Championships will only be hosted where a hyperbaric chamber is reasonably accessible by ambulance, without requiring exceptional transport. CMAS is also committed to developing the organisational and legal framework necessary to implement safety protocols quickly, avoiding obstacles from local medical regulationsâ.
Final thoughts
It seems that Andreyâs tragic incident (and the time it took to treat him) wasn’t necessarily the fault of any single person or organization, but rather a consequence of the current limitations in protocols, treatment, and broad understanding of freediving-specific injuries.
As athletes continue to announce ever-deeper dives, with no sign of a plateau in sight, the hope is that this incident will galvanize a collective effort among athletes, researchers, and medical professionals to talk, research, and work together to make competitions safer, perhaps even one day with the inclusion of officially regulated practices of IWR.
DAN Europe would like to wish Andrey a full and speedy recovery.
About the author
Charly is a writer whoâs originally from the UK but has been based in Dahab, Egypt for the past four years. She taught scuba diving for three years in Cyprus, Thailand, and Egypt before discovering her love of freediving. She still scuba dives for fun but these days sheâs more focused on her freediving training. When sheâs not in the water, diving, sheâs on her laptop, writing about diving.
