A chilly wet morning in early April, driving out of Edinburgh, the windscreen wipers beating hard.

The dashboard display says it's eight degrees. Why did I agree to do this again? I'm heading out to Foxlake Wake Board Park near Dunbar in East Lothian for an exclusive sneak preview of a brand new event in Scotland's calendar of runs, bike rides and triathlons. This one, to be held on June 7, is genuinely unique: a mini off-road triathlon suitable for newbies and secondary school kids but also for serious triathletes.

In June, it will no doubt be delightful, but right now, it's not. The prospect of leaving the nice warm car, jumping into a cold loch for a swim and then hauling myself out before cycling and running in wet clothes around the rest of the track, in this weather, is starting to seem about as appealing as soggy toast.

I have never done a triathlon before, which makes me the perfect guinea pig for the Foxlake Tri, organised by race managers Durty Events (the team behind the Celtman! Aviemore and Craggy Island triathlons). I've done lots of running and cycling but have always been put off swimming outdoors because - hello? - this is Scotland.

I've never forgotten swimming in the sea at Aberdeen beach with my cousin. The photos of us capture the moment we got whacked by our first wave: open-mouthed, wide-eyed shock. It was like having a slushy poured down your back, and that was in July.

OK, so this isn't the North Sea, and I'll have a wetsuit on, but it's still brass monkeys out there, especially in the wind. On the other hand, the event is deliberately short. The cycle is 3km, the run 800m and, crucially, the swim is only 150m - event organiser Paul McGreal recognises that the open-water swim is often what puts people off trying triathlons.

That super-short distance makes the Foxlake Triathlon unique. Triathlons usually come in four distances, from sprint (750m swim, 20km bike ride, 5km run) to the punishing full ironman (3.8km swim, 180km bike ride and a marathon distance run). This will be more of a dash. There will be three separate events, the first a single lap "race" for novices and under-16s. Then - and here's the really cool bit - there's a second solo race which will involve completing the course several times. Entrants will line up in a number of small heats of 20 people, the quicker 10 from each going on to one race and the slower 10 to another. That process of stratification will continue over several rounds, with the fastest triathletes moving into the grand final, and everyone else finishing up in a series of small finals with others of their level.

It will be like taking part in your own Commonwealth Games, complete with cheering spectators. Beginners and veterans alike can take part. "This means competitors can take the race on the rivet [at full speed], or in their comfort zone, have a huge amount of fun and end up in a final that they have a serious chance of winning," says McGreal.

The other option is the 4x4 off-road team relay, thought to be a world first and involving each team member doing the swim/bike/run once before handing over to the next person.

But back to our dreich April morning. First things first: the swim. After getting togged up in a wetsuit, over shorts and t-shirt, it's time for McGreal and I to go for a swim. At one point last summer the water here reached a bath-like 24ºC, by race day it will be at least 15ºC and perhaps even warm enough for wetsuits to be optional, but today it is only just pushing 10ºC.

Whoosh, we're in up to our necks; wow, that's cold - I can feel chill water pouring into my wetsuit through the neck cavity. Keep moving. Once that layer of water warms up, McGreal reminds me, it will feel better. A large green frog swims past. Everything is cold right now, but I have to admit it's exhilarating. My fingers, which are prone to freeze, are actually feeling warmer than in the open air. We tread water and then start our swim, and sure enough, after a few minutes, I can feel my temperature slowly rising. Hey, this is all right. We swim up and down, McGreal going the whole hog with goggles and front crawl, me keeping head above water with a sedate breast stroke, and then, swim complete, I emerge triumphant from the water. Now we're all smiles, the tension gone: that was great; it wasn't too cold after all. I could probably be a Royal Marine if I wanted.

No time to dither, though: wetsuit off, it's time to get on the bike, in wet clothes but with a lovely dry hoody on top. Will the chill set in now? Thankfully it doesn't, because we keep moving.

The ride itself is just technical enough: there are two short, steep-ish downhill sections that require concentration and will please the serious athletes, but nothing to put off a novice. We finish back by the water and then there's a mostly flat run on well-defined tracks to the end.

Foxlake Wake Board Park is a safe car-free environment comprising gentle woodland trails set around a small, shallow man-made loch. It has changing rooms, a cafe and, for a bit of fun between races, Foxfall, a low ropes challenge which involves crossing on ropes between platforms suspended over water. On race day, the whole place will be alive with runners, cyclists, swimmers and spectators.

So what's the verdict? That June 7 is going to be a day of wet, muddy, exuberant fun. As for this triathlon lark, I think I'm probably now ready for the full ironman.

Entry fees: solo £36 British Triathlon Federation members/£42 non-BTF; relay £40 per team of four; single lap race for novices, tristars (11-14) and youths (15-16) £10. Book your place at www.durtyevents.com