A total of 130 competitors from around the globe took part in the 28th World Bog Snorkelling Championships in Waen Rhydd Bog on the outskirts of Llanwrtyd Wells, Powys - the UK's smallest town.
Dineka Maguire from Belleek beat the previous best time by just over a second when she swam two lengths of the 55-metre (180ft) trench in one minute and 23.13 seconds.
The competition even sees some take part in fancy dress for the August bank holiday ritual.
Competition organiser Bob Greenough said: "Dineka has been competing for six years but this is her first year as a senior. I couldn't believe her time.
"We have the serious athletes, who want to prove to their friends they can do it, and people in fancy dress. Part of the fun is making a fool of yourself. One competitor was from Sweden and we had lots from Australia and New Zealand.
"Because the competitors can only use dog paddle, it's all about leg power," he said.
The same two trenches, home to fish and insects including the harmless but nasty sounding water scorpions, are used every year.