This happened last week after reading Roger Deakin’s beautiful book, Waterlog. In the mid-1990s, Deakin was swimming in an old moat outside his farm in Suffolk when he hit on the idea of swimming in as many freshwater places as possible.

He called it “the notion of a long swim through Britain”.

He spent a year at it, beginning and ending in the spring. In her introduction of the new edition of Waterlog that has just been published, Bonnie Tsui — herself a writer of distinction on swimming — has written that the book became a best-seller, inspired the wild swimming movement, and reminded readers “of the rich swimming history embedded in their everyday.” When he went on his year-long swim, Deakin was 53 years old, recently single, and his only child was away in Australia.

But this book is no maudlin meditation on loss and misery. Instead, it is gloriously uplifting in a way that is authentic and meaningful; it’s not selling self-help, but if you read it carefully it is full of wisdom. And, crucially, it is neither propaganda, nor an attempt to give a sermon.

Deakin sets out in a matter-of-fact way how swimming just makes him feel better in body, in mind, and in soul: “Natural water has always held the magical power to cure. Somehow or other, it transmits its own self-regenerating powers to the swimmer.” As he undertook his Odyssey, Deakin was a slave to no convention: for example, sometimes he wore a wetsuit and sometimes he didn’t wear anything at all. Basically, he just did what he wished and lived in the liberation of that pleasure — and from the water he enjoyed a different perspective on all of humanity, including himself.

Deakin wrote about how “you see and experience things when you’re swimming in a way that is completely different from any other. You are in nature, part and parcel of it, in a far more complete and intense way than on dry land, and your sense of the present is overwhelming.”

He gave a great example of how this works: “In wild water, you are on equal terms with the animal world around you: in every sense, on the same level. As a swimmer, I can go right up to a frog in the water and it will show more curiosity than fear.”

For all the years spent in Offaly, I had never thought of swimming in the wild water of the county. But the prospect of looking at a frog to see who might blink first could not be ignored as an idea; what better place to start looking than the River Shannon.

Down at the beautiful west Offaly village of Banagher, there is a riverside park that sits behind a Martello tower. A lovely new tea, coffee, and cake hut, expertly made from an old horsebox and named The Martello, opened last week and is already doing the kind of trade that tells you it will thrive with the swimmers and others who pass its stand.

Stretching out into the Shannon, behind The Martello, is a basic structure of concrete platforms and steel rails, that allows you to swim in the fast-running river. The platforms sit high in the water, and the river runs beneath it and — when boats pass — the water splashes up above the concrete.

There is a strong pull on the pool. The Shannon flows briskly through the arches of the stunning feat of 19th-century engineering that is the bridge at Banagher. So when you’re in the pool, you can simply lie flat on the water and you will quickly find yourself pulled from the top end to bottom.

The murk of the water as it spat and gurgled on its way to the south-west was a reminder of the power of its flows. A further reminder came from the presence along the shore of eight, and then 10, members of the Offaly Sub-Aqua Search and Rescue unit. They were gathering to set off on a training exercise down towards Meelick.

They set off downstream with their diving equipment in a swift launch that pushed waves across the pool. In recent months, training has led to sub-aqua divers finding Bronze Age spears, Medieval swords, a half-dozen Stone Age log boats, and Gallowglass helmets. Finds from more recent centuries include battle axes, shields, and 18th-century muskets and pistols. The discoveries are inadvertent — the men are surveying the bed of the river in preparation for the reality that the day inevitably comes when they have to search the river for missing persons.

In his book, Deakin notes the danger that is present in every swim: “Leaving behind the land, you go through the looking-glass surface and enter a new world, in which survival, not ambition or desire, is the dominant aim. The lifeguards at the pool or the beach remind you of the thin line between waving and drowning.”

There is also the cold. The four teenagers with me threw themselves with a shriek into the river. They proceeded to taunt and sneer for the 15 minutes it took my dignified descent to be completed. It is not easy to retain a state of grace when inching off concrete and slippery timber into cold water, while being splashed and generally mocked.

It is also not made any easier when you catch the eye of a man walking by with his dog, he laughs and says: “It’s hardly that cold! No need to make a production out of it!”

In Waterlog, Roger Deakin wrote of a swim in the North Sea on Christmas Day, when there was “driving rain and breakers the colour of dirty knickers licking up the beach.”

He struggled into the sea wearing only speedos, defying the press of the water, and then fully immersing himself: “I experienced the intoxication of the fiery cold, and found myself splashing about and even body-surfing with manic energy.” Afterwards, burning with a bright purple glow, he recovered his warmth through bowls of onion soup.

In that pool in the River Shannon, immersion, long-delayed, was worth the pain. It was not nearly as cold, of course, as the North Sea on Christmas Day, but neither was it a nicely-drawn bubble bath. Nonetheless, once the initial shock was conquered, the water was first bearable and then genuinely lovely and fresh — it performed the feat of feeling different. This was what Deakin called “the sensuality of swimming in your own skin”.

As for the nature on view, there were no frogs. But there was a ladybird. It sat resplendent on a small bunch of reeds that floated against my nose. There was no time for introductions.

And there were the fish that scuttled along the surface, dancing up out of the murk and disappearing as quickly.

There was no need to stay in too long — that would have been showing off. But in the afterglow there was a real sense of achievement. The teenagers were still in the water and for all the legitimate talk about how much life has been changed by the interconnectedness of the digital world and the always-on presence of mobile phones, this was also a happy reminder that there are some things that still transcend technology. Roger Deakin understood this as a choice between reality and virtual reality.

Before they were even dry, the teenagers began to plan a return trip. They also made lists of other places they could go and swim, and their compilation included two lakes, the Grand Canal, and beaches on both sides of the island. No place of chlorinated water was mentioned; swimming pools seem to have dropped from their consciousness.

I mentioned that I have been reading a book about swimming and I told them some of the great sentences I’d read in it, like where Deakin describes seagulls as “nature’s bagpipes” and explains why the skin of an otter never gets wet in the water. For some reason, they seemed not to be able to hear.

And I didn’t even get to the part where Deakin laments how powerful vested interests too often restricted public access to wild water, how glorious old maps record longstanding use of natural springs and baths now lost to the public.

But the glory of the book is in the impulse it gives to swimming in a different way. It lies in the words where Roger Deakin reminded his readers of the most basic of salient facts as to why swimming feels so good: “When you swim, you feel your body for what it mostly is — water — and it begins to move with the water around it… When you enter the water, something like metamorphosis happens.”

- Paul Rouse is professor of history at University College Dublin.