And they were served chips by a mermaid host while they competed at Ponds Forge in Sheffield, on Saturday.
The game was organised by 46-year-old scuba dive master John Stanley to raise money for Macmillan Cancer Support after his wife Gina died in May following a battle with endometrial cancer.
“We started planning [the event] together and I so hoped she’d be able to see it happen,” said Mr Stanley, of Hillsborough, Sheffield, “but it wasn’t to be. She was 44.
“I had the idea in bed when I couldn’t sleep. I wanted to do something to raise money and I thought what do I like doing? Diving and playing poker, so I combined the two.”
Mr Stanley, who dealt cards at the weighed-down table said before the underwater tournament: “The divers will have to make sure the reduced oxygen doesn’t mean they start making rash decisions.
“On the plus side, wearing breathing apparatus should make it easier to keep a poker face.”
Specialist cameras relayed the two-hour session to a pool-side audience, while diving instructors were on hand to take people down to watch the action live.
The six players – Scott Bailey, Mark Cullumbine, Mark Jeffs, Rob Timmins, Tim Martin and Dan Hamilton – are all from Sheffield.
Mr Stanley hopes that in future, it could become an annual event.