The public footpath lay barely 20 metres from where I stood, promising a stroll along the river, passing fields and through woodland, well away from any road. Yet there was something in my way blocking access to it. The very river it meanders alongside – the Thames – flowed between me and this legally designated right of way.

I checked my Ordnance Survey map of this part of Berkshire to see how to reach the path, but there was no other footpath that would legally lead me to the island on which it sat (a bridge I spotted was not a right of way, with a closed gate). This was a permitted pathway that no one could actually access, unless they had a boat.

It was this path that came to mind when, a few weeks later, I heard about a new activity growing in popularity across Britain, one that combines water and walking: cross-country swimming. This is when hikers and walkers carry a specially designed, large but lightweight waterproof tow-float and a dry bag. So when you reach a watery obstacle you can simply take out your cossie (or more likely wetsuit) and swim it.

This activity was born out of lockdown, when pools were closed and people’s movements were limited. It is the brainchild of two brothers, Will and Tom Watt, the latter of whom I met at Grantchester Meadows in Cambridge to be shown the strokes, along with a small group of other curious water lovers.

“We spent a lot of time in the Lakes growing up,” Tom said as we ambled along surrounded by the buzz of grasshoppers, the flutter of butterflies and the chirp of birdsong, while the River Cam babbled happily by. “There you’d come off a hill and want to climb one on the other side of the valley but a body of water was in the way. It would be an eight-mile walk to get around it or,” he said with a smile, “a mile-long swim. It was then we came up with the idea.”

The Watts spent some time trialling a variety of kit to find out what could make this activity possible, including existing flotation aids and dry bags, but found nothing that could adequately incorporate everything needed. For a while they focused instead on events: they created the Swimmer, a central London half marathon that takes in the city’s ponds, pools and parks. But 2020 gave them the opportunity to work on the perfect cross-country swimming pack and launch it with a retreat in Devon, which they promoted as “epic adventures over land and water”. It all sounded fun in a Type 2 way (miserable while it’s happening but pleasurable in retrospect), but what about those who are after less endurance and more enjoyment?

That’s where this route comes in. It’s a relatively easy half-day trip that Tom’s company, Above Below, runs throughout the summer to satisfy the demand from less hardcore swimmers. Beginning at Cambridge railway station, it meanders along the Cam for 5km to the Orchard tea room, where the likes of Virginia Woolf and Rupert Brooke wrote – and took dips. We would be doing the same (minus the writing for most, although not for me), completing a wonderful wet and dry circuit by swimming back with the current in the Cam.

As wild swimming becomes more popular (it predictably experienced a boom when restrictions were applied to gyms and pools), it began to run up against obstacles, and this stretch of the Cam is a case in point. Earlier in the summer King’s College, which owns the land, tried to ban the activity here – even though it has been enjoyed at Grantchester Meadows for at least five centuries – citing unruly behaviour and littering. Protesters have fought the ruling and, for now, the practice is still being enjoyed while discussions take place between swimmers, council and college.

The scent of freshly baked scones and brewing tea mixed with the notes of elderflower and freshly cut grass as we reached the cafe. After chatting about some of Tom’s watery adventures (including a crossing of the Lakes, the Broads and the islands of Scotland) we walked to the edge of the river and changed into our wetsuits. It was then that Tom revealed his crucial invention – the RuckRaft.

This is a device a bit like a large inflatable horseshoe, with the raft made from a toughened material that means even when holding towels, drinking water, dry clothes and snacks (anything up to 15kg) in the attached dry bag, it still glides on the surface of the water effortlessly.

As I plunged into the river, its coolness welcome in the humidity of an August day, the weight of my supplies dissipated. My back was free, and I simply pulled everything I needed behind me, feeling almost weightless.

I relaxed into the water, my hair flowing around my face as I slowly floated alongside dragonflies, a moorhen and her chicks, and a curious grey heron – none of which seemed to even acknowledge my presence.

The whole experience drifted by all too quickly and in no time I was drying off and walking back to the station feeling buoyed. Though cross-country swimming was invented to provide a challenge, I believed it had given me something much more important – the confidence to try it by myself.

So I decided to return to my inaccessible island, the footpath by the Thames. I headed to the Ferry Pub at Cookham with my new bit of kit (I couldn’t resist investing in a RuckRaft), along with a backpack full of dry clothes, a camping stove and picnic, head buzzing with excitement. I was about to reach that floating footpath.

I plunged into the waterway and swam across to the eyot, exploring its banks for a while. After five minutes of searching, the island relented: I found my entrance point alongside a tree and hoisted myself out.

A quick dry down and change of footwear later – from neoprene boots to sandals – and strapping my RuckRaft to my still-dry backpack, I finally trod this trail. Blackberries festooned the hedges and I foraged hungrily alongside robins, sparrows and wagtails. At first the footpath was overgrown but, as I neared the lock, it became a joyous straight line edged by crowdless fields and overarched by trees. Until, as simply as it had begun, it ended at the water’s edge once more.

I changed again and swam farther down the river, taking in the section that runs alongside Cliveden en route to Maidenhead. It was as beautiful as it was when Jerome K Jerome paddled it in Three Men and a Boat – “In its unbroken loveliness this is, perhaps, the sweetest stretch of all the river,” he wrote – lined now, as it was then, with the chalk hills of the Chilterns, and canopied with oak, sycamore and beech. Red kites glided above me as I backstroked so I could look up at the woods.

Halfway down I took a break on an island and made tea, courtesy of my camping stove, in a place I wouldn’t have been able to reach had I been walking only. Then it was back in the water until, just before reaching Maidenhead, I hauled out, dried off and walked the Thames Path back to the start, my smile almost as wide as the river I was strolling alongside.

“The idea,” Tom had explained to me back in Cambridge, “is that people will use the RuckRaft and the idea of cross-country swimming to forge their own routes and share them with others. To enjoy water as part of their day rather than worry about it causing an unnecessary diversion. And to open up more of the countryside to walkers and swimmers.”

Certainly, both in Cambridge and in Berkshire, my newfound skill had given me the chance to do just that. Though the Thames loop wasn’t that long a walk, and the swim not too challenging, it represented more than that – the chance to pioneer a new route never open to me before, the opportunity to reach a picnic spot that otherwise would have been off-limits and, when it came to that footpath, the ability to access the previously inaccessible.

• Above Below runs cross-country swimming events, retreats and day experiences. Upcoming three-day retreats in Devon (July and September, from £324) and Ullswater (September, from £328), include accommodation, food, instruction and local transport