Competitive freediving is exhilarating for adventurous divers, who at the same time are perilously exposed. Trainers have enough respect for the sport to even caution it as “dangerous,” despite divers’ desires to plunge deep into water that gets darker by the meter.

That exhilaration, though.

“Freediving in general is an adventure,” world record holder Alexey Molchanov said in a 2017 interview with professional freediver Adam Stern. “Any sport can be for people who just want to enjoy it. And the recreation levels of freediving is even more because it’s open water. … It’s more about exploration.”

To date, no freediver has reached a deeper depth than Molchanov.

The Russian in 2017, at the age of 30, in the water in Long Island, Bahamas, used a monofin and single breath to dive to a depth of 129 meters, which remains the world record in competitive freediving’s “Constant Weight with Fins” division, or, CWT, as recognized by the International Association for the Development of Apnea (AIDA), which regulates the sport of freediving. CWT challenges divers in a race against depth, time and unaided oxygen to go as deep as possible with the use of fins or a monofin.

During his record descent, Molchanov ceased his monofin’s dolphin-like kick at 58 meters (and 61 seconds) into his plunge, at that point allowing the current to sink him in a natural freefall at a rate of about a meter per second. At 2 minutes, 12 seconds into the plunge, on a single breath and now at a depth of 122 meters, Molchanov for the first time reaches for the guide rope and kicks a final burst to reach his record depth before beginning his turn upward. His monofin kicking then starts anew, this time for the ascent.

Very calmly Molchanov eventually resurfaces to a sea of above-water cellphone cameras waiting to capture the moment after he spent a grinding 3 minutes, 56 seconds underwater on a single breath.

He’s calm and collected.

And yet the danger has been there the whole time.

“The pressure on a diver increases … every 10m he or she descends,” the National Center for Biotechnology Information notes in Peter Wilmshurst’s article “Diving and oxygen.” “An average healthy person with no special training can hold his (or her) breath for about half a minute. During the breath hold the oxygen content of tissues decreases, but the breath hold is broken as a result of carbon dioxide production and resulting acidosis, which stimulates the respiratory centre. With practice you can resist the stimulus to breathe for longer but it remains carbon dioxide accumulation that causes release of the breath hold.”

The extreme sport suffered a tragic blow when one of its most accomplished divers experienced the ultimate risk.

Fellow Russian Natalia Molchanova still holds two AIDA world records, including a remarkable feat of 237 meters in the DYN division, or, Dynamic Apnea with fins, in which competitors swim underwater as far as possible (as opposed to diving as deep as possible) with the use of fins or a monofin on a single unaided breath. Molchanova’s record-breaking swim in September of 2014 kept her swimming nonstop underwater using a monofin for 3 minutes, 33 seconds.

Tragedy struck 11 months later, however.

While freediving in the Balearic Sea, close to the Spanish island of Formentera, the then- 53-year-old Molchanova submerged but never resurfaced. Despite recovery efforts, her body was never found, and she was presumed dead three days later.

“She was diving without fins to around 30m to 40m and supposable got into strong underwater current,” a joint statement issued by Molchanova and AIDA stated. “She disappeared while diving.”

As the extreme sport of freediving gains attention and a following of adventurous underwater challengers, so to come cautious warnings and heedful urgings to train, especially to first employ “dry training” breathing techniques on land.

“Freediving is in many ways a very safe sport,” freediveuk.com instructs on its website, “but without formal training it can be dangerous.”

As for the monofin itself, its pure speed is the official rage of the world of swimming.

The 50-meter races are so fast, in fact, that swimmers, in one format, spend the whole race as underwater rockets. A center-mount snorkel is used for surface races; a small pony-bottle for sub-surface immersion events; and no breathing aid is used at all in breath-hold, or apnea, underwater sprint races.

Surface races feature distances of 50, 100, 200, 400, 800 and 1500 meters. When not racing individually, swimmers can team up for 4×100 and 4×200 relays.

“It’s quicker, it’s faster,” Anna Azhanova, World Underwater Federation president, said in a 2017 interview with the Discovery Channel, sizing up finswimming against traditional freestyle lap racing. “In a short distance it’s about 50 percent faster than swimming.”

According to Fédération Internationale de Natation (FINA), the current world record for the standard 50 freestyle long course is 20.91 seconds, set by Brazil’s Cesar Cielo in 2009. Conversely, Confédération Mondiale des Activités Subaquatiques (CMAS) has the current world record in the finswimming 50-meter (achieved with a monofin) as 15 seconds flat, set by Columbia’s Mauricio Fernández in 2016.

“I should have just done this all along. What the hell was I thinking?” the United States’ Michael Phelps, the most decorated swimmer in Olympic history, joked with Discovery about finswimming.

The sport has been a part of the World Games circuit since the early 1980s. CMAS – founded in 1959 and today comprised of more than 130 federations from five continents – will sponsor two World Cups in 2018, one in the United States and the other in Germany, among the six scheduled events in the calendar year, including Junior competitions.

Finswimming has yet to gain much traction, though, as an Olympic sport. The Olympic Programme Commission in its International Olympic Committee (IOC) 2002 report, nixed the idea of adding finswimming to its lineup.

“Statistics reviewed on federation affiliation, nations competing in major events and broadcast and press coverage of major events for most requested sports did not indicate a higher level of global participation and interest than sports currently in the Programme,” the report stated, “and therefore could not be considered to bring additional value.”

At last glance, even a Facebook page literally called “Finswimming to the Olympic Games 2024” to take up the cause hadn’t posted any new content in seven months.

But Davide Manca, an Italian writer with finswimmer.com, reports that underwater sports may yet get a renewed push for inclusion in the 2024 Olympic Games in Paris. “One of the reasons to think about the return of apnea to the Olympic Games in Paris 2024 is that: Underwater Sport was at the Olympic Games in Paris in 1900 where an event was held called ‘Underwater Swimming,’” Manca reports.

Meanwhile, as the sport rapidly pushes forward, Russia’s 31 gold medals in finswimming and 66 total medals currently lead the world.

Some of the up and coming finswimmers are catching on fast since they’re strapping on the fins as children, bypassing even standard freestyle when they first get into the pool.

“When I was 6 years old I began with (finswimming),” 18-year-old Adam Bukor, of Slovakia, said in an interview with the Polish Underwater Federation during the 2017 XII CMAS Finswimming World Cup in Poland. “There wasn’t anything before it for me. My first big competition was maybe six years ago as a very young child. It was such a big thing for me, of course. I was the youngest maybe. … It was the beginning of my career actually.”

He has since become a four-time world champion and three-time record holder.

“It’s very fast,” Bukor added. “It’s much faster than normal swimming.”