British Sub-Aqua Club's anniversary dive off Holyhead
A group of 60 divers will mark the 60th birthday of the activity's governing body with an "underwater party" off the coast of Anglesey.
The divers from across north Wales and Cheshire will be swimming down to the wreck of a cargo ship lost in 1886.
The American steamer Missouri lies in 60ft (18.3m) of water at Porth Dafarch, near Holyhead.
It is one of a series of 'Diamond Dive' events to mark 60 years of the British Sub-Aqua Club.
"I think we all want to celebrate BSAC's Diamond Jubilee and getting together and diving on the Missouri is an ideal way to mark the anniversary doing what we do best - diving," said Ken Oakes, president of the Flintshire sub-aqua club.
"It's a brilliant idea and should be a real experience. I hope we have some decent weather - it should be quite an underwater spectacle if the visibility is good."
The Missouri went down during what was described as the most violent snow storm in two decades on 6 March, 1886.
The ship, a 3,000 tonne iron screw steamer, hit a rock about a mile from South Stack lighthouse at Holyhead.
It had been travelling from Boston in the US, carrying nearly 400 cattle.
All the crew were saved, but some 270 of the animals drowned when the vessel capsized in the following days.
Steve Ellis, Wrexham sub-aqua club's training officer, said club members were really keen to join their colleagues from clubs at Chester, Crewe, Gwynedd and Rhosneigr on Anglesey to tackle the Diamond Dive on Sunday.
He said: "It's a superb idea and something we really wanted to support. It will definitely be a unique experience and we are all really looking forward to it."