“Swimming in the wild, outdoors and without a roof over your head, is now a mildly subversive activity... It certainly appeals to free spirits...”

I DIDN'T feel terribly subversive, sitting on a small boat in the Dalmatian islands, and passing round my suncream-smeared copy of Waterlog, Roger Deakin's love letter to swimming, from which the above passage is taken. But there were definitely some free spirits among the 15 of us, mostly couples and singles in their 20s and 30s, on this swimming holiday organised by the specialist operator Swimtrek.

There was Emily, whose earlier Swimtrek trip had inspired her to become a triathlete, and who would go for a 4km (2.45 miles) run before breakfast. Richard and Helen booked the trip before realising Helen was pregnant, and so turned it into their honeymoon. Vicki had shooed her partner off home after the first part of their break as he didn't share her passion for the water. Siblings Kate, Nancy and John kept up a teasing banter all week. And 18-year-old Anna, the youngest in the group, was one of the fastest, but so slim she needed a wetsuit to stay warm, despite the 24C (75F) water. This was not a problem for the rest of us, I was pleased to note: while most of us were regular pool swimmers, nobody looked as though they were training for the Olympics.

We were based at Hotel Maestral in Prvic Luka, one of two villages on sun-bleached, car-free Prvic island, 45 minutes by ferry from the bustling town of Sibenik. The first evening, we swam 800m around the bay so we could be split into groups according to speed. For safety reasons the slowest group (the “Scenic Swimmers”) would set off first, with an inflatable dinghy alongside. The middle and fastest groups (the latter, all women, known as “Team Barracuda”) would head off at later intervals. Our support boat, captained by the chain-smoking Jadran, brought up the rear, the idea being that we would all finish together. “It's not a race,” said the no-nonsense Claire, one of our guides, assigning me firmly to the Scenic Swimmers.

Next morning, over breakfast of eggs, fruit and coffee on the Maestral's harbourside terrace, Claire and fellow guide Lizzie gave us a safety briefing. Then we were off. Our first swim, 2km, took us from Separina - the other village on Prvic - to the island of Tijat, and gave me a sense of whether I could keep up. The first shock was the buoyancy of the salt water. You float higher, so swimming is easier and treading water is effortless. This was useful, as we regularly had to gather together to wait for group members, or swim up to the support boat from which Lizzie or Claire would throw bottles of energy drinks to us.

The second shock was the taste - I soon had a furry tongue from the salt water, which was unpleasant, although we all got used to it. And yes, I could keep up. My front crawl was slow, but steady. Also, I have learnt to breathe on either side, which turned out to be vital when the water was choppy, helping me to breathe away from the waves.

Soon we bonded into our groups, and learnt to keep together for safety. Once Lizzie pulled our group into the dinghy; out of the path of a badly crewed yacht, since these calm waters attract amateur sailors. We all politely averted our gaze from one unfortunate's torn Lycra - there's really nowhere to hide if your swimsuit rips.

But most of our swims were in quieter spots. We usually did two 2km swims each day, but a highlight was a 4km river swim in the Krka National Park - it took me 1hr 45min, but afterwards I was glowing with energy.

Of course, all the exercise meant we could eat as much as we liked. For lunch, Claire and Lizzie would whip up salads, including plenty of potato and pasta for energy. One day we even got Jadran into the water - he dived for mussels, then cooked them for us. In the evenings we devoured pasta, fish and pizza in Prvic Luka or at an excellent seafood restaurant, Ribarski Dvor, in Separina. A huge bowl of seafood pasta was about £4.

The fact that Croatia is such good value is one of the reasons Swimtrek introduced trips there in 2005, explained the company's founder, Simon Murie. Also, he said: “The Dalmatian islands are a lot less touristy than comparative islands in Greece. Tourism on the Dalmatian coast is growing, but most people go south of Split towards Dubrovnik, not north towards Sibenik and the islands where we're based. They are really popular with the sailing crowd, too.”

By the end of the week, I was dropping into bed by 9pm, exhausted and aching gently from all the exercise. Over a beer one evening we swapped notes, agreeing that while Roger Deakin might have been writing about swimming in Britain, he captured the sense of camaraderie shared by all keen swimmers. When telling friends we were taking a swimming holiday, the response was usually one of astonishment. Yet tell someone you are going sailing or skiing - which require far more time, money and training than swimming does - and they don't bat an eyelid. Potty, really.

In the heat of a Croatian summer I could think of nothing more delightful than jumping into a warm, calm sea. As I struck out towards our next landmark, a large cross on top of a hill on the island of Kaprije, and saw the sunlight filtering down through beautiful, clear water, I knew I had chosen the right trip.

Need to know

Swimtrek (020-8696 6220, www.swimtrek.com) offers a week in Croatia next summer, based at Hotel Maestral on Prvic Luka, from £695pp, including all swims, breakfasts and lunches, but excluding flights and evening meals. Single supplement, £100pp. BA (0870 8509850, www.ba.com), easyJet (0905 8210905, www.easyjet.com) fly to Split.

Further information Croatian National Tourist Office (020-8563 7979, www.croatia.hr).

Reading Waterlog by Roger Deakin (Vintage, £7.99)

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