There are several such dips held around Europe, but the largest is organised by the Red sky Foundation and Lions Club of Sunderland, England.
The swim in Pembrokeshire, Wales, started in 1970 and has become Tenby's main Christmas attraction, with around 600 swimmers and thousands of onlookers each year.
Started by the Tenby Sea Swimming Association (TSSA), the Osborne family has been associated with the spectacle from the beginning and Chris Osborne, chairman of TSSA has seen the event take place in every weather condition from brilliant sunshine to freezing wind.
The event continues to be one of the year's biggest social gatherings of the club, with members travelling from far distances to participate.
Several charity swims take place in East Anglian resorts on Christmas and Boxing Day.