The 12 from Galashiels, including a previous virtual non-swimmer, will plough through the bracing three- mile length of the loch in one-mile relays on Saturday.

And they hope, along with a charity golf event, to raise thousands for Prostate Scotland.

Organiser Gillian McCrirrick said: "We're feeling quite anxious but we're looking forward to the challenge and hoping it's not windy on the day."

For a few of the group it's their fourth year of fundraising, the first of which involved completing the Machu Picchu trek in Peru for Action Medical Research. Others have joined this year specifically for the watery challenge.

Gillian said: "We pick a different charity every year and we've raised £30,000 so far. We chose Prostate Scotland because we felt it hadn't had much of a profile. No-one in particular (in our group) has been touched by it, we just felt it was a charity that could probably do with a bit of a boost in funds and we are keen to keep it local."

All the money raised for the national charity will be spent in the Borders.

For Timmy Lamb, Saturday's swim will be a huge achievement.

Gillian said: "He had only managed to swim a couple of lengths, maybe 100 metres before: this has been a big challenge for him."

But none of the participants are swimming champions.

"I have swum for fitness but nothing really extreme and most of the others haven't really either. There are no swimming club members, we're all amateurs," said the massage therapist.

"It was my idea, which on reflection ... Well, the reality is we have been up a couple of times and got into the water and it's dark and very cold: it's a challenge for a lot of us!"

The team of 12, who have a coach, David Scullion, will be supported by Galashiels pool lifeguards, Selkirk Canoe Club paddlers and the loch's angling club.

The swimmers range in age from their twenties to their fifties and some are hoping to complete the full 3.3 miles as individuals.

The team of Ian Thomson, Elaine Turnbull, Duncan Sinclair, Bruce McClory, Danny Kelly, Timmy Lamb, Alistair Douglas, Wilson Jamieson, Kay McFarlane, Donald McNeil, Scott Cranston and Gillian has been training since February and the swimmers try to train together at least one day a week.

But a scheduled practice swim in the loch last Thursday had to be cancelled - because of forecast lightning.

Tibbie Shiels Inn is putting on a paid barbecue for the paddlers and their supporters on Saturday.

Meanwhile, the Charity Texas Scramble golfing event next month in aid of the same charity is open to teams of four. For more information contact tibby.thomson@02.co.uk and for further information on prostate cancer go to www.prostatescotland.org.uk