This swim, in three parts, is mostly set on a beautiful day, and in the stunning Snowdonia national park. There is a small cast: me, artist Vivienne Rickman-Poole, some distant climbers, and a few animals.

Part one

Vivienne parked her van by a hillside farm at the north-west edge of the national park; as we got out, a peacock strutted and a llama kept imperious watch over the land. The bird looked flamboyant but the llama fitted right in, like a sheep adapted for look-out duty. We set out on the kind of walk that made me remember holidays of the past, wielding OS maps.

A rutted track, ladder stiles, hopping from tuft to tuft in warm boggy bits and easy-clambering down rocks. It was about 15 minutes before we had sight of the twin lakes Llynnau Cwm Silyn and a further 15 minutes to get there. The nearer lake was longer and thinner, the further one, our destination, a bowl cupped in the shadow of a mountain. “It looks glacial,” I said. “I think the name means ‘Lake of the Spawning,’” Vivienne replied. “Oh,” I said, a little bit distracted by that idea.

Facebook Twitter Pinterest Jenny explores the Snowdonia landscape

Part two … in the water

We’d passed other lakes on our way here but none were quite “it”. This bowl-shaped one, however, was it, and Vivienne would know: swimming the lakes of Snowdonia has become her thing. It may be a lifetime’s work, her dining room is wallpapered in maps. Her current obsession (her word) are the orange lakes, tinted by the ferrous rocks they ride. Today though, she’d chosen Llynnau Cwm Silyn not for the colour – dark blue – but for its crystal clarity. It was startling; I could see every pit and knob of underwater rock where it was shallow.

I’m not interested in temperatures, I’d rather just feel it on my skin. Vivienne Rickman-Poole

Vivienne has a thoughtful, self-contained presence. In contrast, by the time we were ready, I was positively fizzing.

“You look like a mermaid,” I yelled as she slid in to the lake, then sighed at my own cliche. I don’t even like mermaids. I followed her, trying to copy her cool ease but half fell and went “ooof” as I hit the water.

“I’m not interested in temperatures,” Vivienne had said, “I’d rather just feel it on my skin.” It felt sharp, cold, blissful on walk-sweated skin. Crisp and delicious like the best of apples.

Facebook Twitter Pinterest Jenny, left, and Vivienne prepare to brave the waters.

We swam out of the shadows and could see to the bottom, which looked like soft furnishings. “Like it’s covered in hessian,” said Vivienne. We swam to, but not through, a neat bed of eager dancing weeds, liking how they looked but not how they’d feel on our skin. I swam away, dived under and saw Vivienne below water as sharp as a pin. We chatted as we went round, she took photos. “My camera,” she said, “is a really important side of it for me. The creativity and swimming go hand in hand.”

We talked about community and how that is perhaps the one thing she misses from her solo trips round Snowdon’s lakes. But being alone, she said, “Means I don’t hand my power to someone else”. I was reading The Power by Naomi Alderman [her fourth novel where women have power over men] on the train here – it all fitted.

Facebook Twitter Pinterest Jenny and Vivienne swimming in the lake

“I always feel a frisson of anxiety about getting in,” said Vivienne, but “I make decisions and I live with them, right or wrong.” We talked about how going it alone would not be the right choice for some people, me included.

We swam some more, without a plan. I thought I heard the hum of an engine but it was a ticking stream entering the lake; I looked up and saw a few of them, silvering the scree of the mountainside like slug trails on a wall. And then I felt I should get out before the cold took hold. It was too soon, it always is.

As we left the water a fish jumped, reminding us of the name of this lake, and who it belongs to. We started to dress and heard voices in the distance. Vivienne looked, her eyes better attuned to spotting climbers. “There,” she pointed and I saw a tiny flash of red. I wondered if they’d heard us, too, or seen us as little dots in the blue all the way down here.

Part three … happened after we’d gone our separate ways

Facebook Twitter Pinterest Jenny Landreth’s favourite shot taken by Vivienne at Llynnau Cwm Silyn

Vivienne’s approach to swims is to “Drop herself into it without knowing all the statistics, or all the folklore.” In the water, she wants “The clarity of thought, to be in the moment” (we both skirt the word mindfulness … mindfully). For her, “part three” is the research afterwards, the reflecting, her “compulsive desire to share”, all of equal importance.

For me, part three came when Vivienne sent me some of the photos she took. One photo was half sky and mountains, half below the water – and a body in the distance swimming down. It could be anybody, but it’s me. It’s a wonderful shot and it’s wonderful to be the body. I can relive the experience from a different perspective, I can reflect and share. That clarity! When I look at it, everything is elevated. I won’t come down for a while.

• Travel and accommodation – at Ty’n Rhos Country House, Llanddeiniolen (doubles from £90 B&B) – were provided by Visit Wales

Jenny Landreth is author of Swell, A Waterbiography (Bloomsbury Publications, £8.99)