By Agence France Presse
Invented by British navy divers in the 1950s, the acrobatic six-a-side sport requires participants to hunt a heavy plastic puck and hit it into their opponents' net with a short curved stick.
Competitors wear snorkels, fins, ear protectors and gloves, resembling a school of fish as they swarm around the puck, diving and somersaulting to gain possession.
The sport has built up a loyal fanbase in Canada, Australia and South Africa and has spread to Asian countries in recent years, including China and Malaysia.
Hong Kong's amateur team, which has around 25 active players, draws from all walks of life, including teachers, an artist, a pilot and geologist Henry Chan, who founded the club which is nicknamed "HK Typhoon".
A former competitive swimmer, Chan, 28, learned to play the sport while studying in the US.
He decided to set up a Facebook page seeking fellow fans on his return to Hong Kong in 2010 as he missed playing what he describes as a "fast-paced and three-dimensional" game.
"I started receiving messages from veterans from all over the world who had transferred to Hong Kong to work. They have a lot of experience in playing, teaching and even competing at the highest level," Chan told AFP.
Chan's Facebook group is followed by nearly 200 people and his fellow Hong Kong players have now formed a competitive team, taking part in their first tournament in May last year.
They came third out of 11 Chinese cities that participated in the China Cup in Chengdu.
The team's long-term aim is to secure a place in the underwater hockey world cup -- but for now they are setting their sights on this year's China Cup in May.
"We are aiming for the first prize and I'm very confident about it," said Chan of the upcoming tournament in Hangzhou.
- 'Like dancing' -
The Hong Kong team practises once a week at a 25-metre school pool, working to improve their power, endurance and lung capacity.
Experienced players swim whole lengths without coming up for air in training, to help when they dive to chase the puck.
But head coach Nowie Ignacio Cornelia, from the Philippines, says the skills do not come easily.
"Being great comes with time. Your muscles have to get used to being underwater," said Cornelia, 37, who is a freelance cinematographer.
"The key ingredient is to be very calm and relaxed," Cornelia added.
But Chan says it is cooperation that is the key. "There are six (opponents) to defeat before scoring," he said.
"You have to make good use of your teammates and you should really be passing the puck around, take a breath, advance to a better location quicker and receive the puck again."
Out of the pool, the team reviews tactics and analyses underwater footage, along with visits to the gym.
But while there is a hard core of enthusiasts in Hong Kong, Chan says he would like to see more awareness of the game as well as technology and pools designed to help spectators engage fully with the sport.
Team member Flora Tang, 31, said that while water polo and scuba diving were well-known in the city, underwater hockey was still a mystery for most.
For her, it is a welcome escape from her day job in sales.
She said: "I enjoy the underwater feeling. It feels like you're dancing."