More than 150 competitors are preparing for one of the strangest international sporting events, the annual bog snorkelling championships.
Snorkellers cannot use conventional swimming strokes
The contest, to swim two lengths of a water-filled ditch in a mid Wales peat bog, is held at Llanwrtyd Wells, the UK's smallest town.
Competitors must complete the muddy and reed-filled course without the aid of conventional swimming strokes and this year face a strict time limit to reach the first turn.
They have just one minute 30 seconds to reach the first turn.
Philip John, of Bridgend, south Wales, is defending his titles as world champion and young champion against entrants from as far afield as from Ireland, America, and Australia.
One person who may have an edge is Andrew Parker, who last year lost out on the local champion title to his brother by just 10 seconds.
This year, however, he has donned his snorkel, mask and flippers to have a sneaky trial run over the 60-yard course to see if he can beat the world championship time of 1m 39secs.
He said: "The organisers have asked me to clean the trench on Friday in preparation for the competition," he said.
"I will take advantage by having a sneaky paddle up and down the trench, and I will not tell my brother I have done it."
The event began in 1986 when local pubgoers were trying to think of a way to raise money for charity.
Funds from the event will be donated to the mid Wales division of the Cystic Fibrosis Trust.