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It's only in its second year but already the number of people who'll be jumping into freezing water for the Great East Swim's double what it was last year.
3,000 swimmers from our region will be doing the mile long course for charity today in the Alton Water reservoir near Ipswich.
Olympic swimmer Mark Foster, who is from Southend, is taking part.
He told us: "It's my first open-water swim - I've been used to indoor pools for 30 years - but I think I can do it in 20 minutes."
"My advice is: the quicker you get in the quicker you get out, and follow the person in front's feet so you don't need to look where you're going!"
For those who don't fancy braving the water there is an event village with a local farmers market, big screen, Dance East performance, charity village, climbing wall, trampoline, and library.