Swimmers are preparing to pull on their wetsuits and dive into the River Thames on Saturday for the historic Boulters to Bray open water swim.
More than 150 people have signed up to take on the challenge which made a return last year following a 40-year absence.
"It is 20 per cent bigger in terms of numbers," said co-organiser and member of Maidenhead Rowing Club, Keith Dixon.
"There has been a lot of effort in the past few weeks."
Formerly known as the Long Swim, it dates back to the 1800s and was a highlight in the town's sporting calendar.
"It is about doing something different, being outside in the elements with nature," added Keith.
"It is a brilliant time of the day, if you are there at six 'o'clock in the morning there is no traffic or noise, it is lovely."
The 1.7 mile route sees swimmers of all ages jump into the freezing cold water of the Thames at 6am at Boulters Lock in Maidenhead.
They must then battle their way through freezing waters to reach The Waterside Inn at Bray.
First timers will be joined by veterans of the event including 78-year-old Mike Hughes who won the swim in 1968 and also took part last year.
Competitors must wear a wetsuit and be capable of swimming 80 lengths of a 25m pool.
Categories include open, masters 49 plus and junior 15-18.
Entry is £32.
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