There’s a river that runs through my dad’s dairy farm in Devon called the Culm. My brother and I would start swimming from one end of the farm, where there’s quite a deep, narrow section, then hover underneath the humpback bridge, treading water and shouting so that our echoes were amplified. After that, there was a long, rocky section which was knee-grazingly shallow, then we’d swim into a place named Eel Corner, a name I think my brother made up but which managed to terrify himself as well as me, and then you turned round a bend and there was a waterfall, so you had to swim really hard to get out on the bank or you got tipped over the edge.

As I grew up, I just carried on jumping into water whenever there was an opportunity. At Oxford I’d lead expeditions to break into the lido and go midnight swimming. And I remember walking across Scotland and coming across these lochs, and we just had to get in.

One weekend we decided it would be fun to go off and swim Wastwater in the Lake District. It’s the deepest lake in England — 260ft. I remember driving for about seven hours; it was blowing a gale, and it was raining so hard that not even the walkers were out.

But once we got into the lake, it was just magical. When you’re at eye level with the water, you get to see this sort of mist that’s not visible when you’re above it, and you can see that as each droplet of rain lands on the water it bounces, which is just stunning. Wastwater has water that is very soft against the skin and quite cold. When you swim into the middle you’re surrounded by 360 degrees of soaring mountains and sky.

So we went for our swim, and then 15 minutes later — and this is why I love swimming — we got out and were completely happy. The whole nightmare of getting there was behind us. We’d forgotten all about the journey. The weekend had begun.

But rivers are my particular love, and the Thames most of all. I like the buoyancy of sea water, but salt water gets quite harsh after a while. If you do a long salt-water swim, your tongue swells up in your mouth, and your lips get quite sore, whereas in rivers and lakes it’s like going into a mild mineral bath. I love the silkiness of river water, the earthiness of it, and the sensation of being carried downstream by the current: if you stop and do nothing, the show continues. And being so close to the banks, you’ve got this permanently changing landscape. You can be floating along underneath the branches of a willow tree, or bobbing right up to the lilies as you go past, and seeing the cows on the bank — from water level they look as big as elephants. In spring there are 70,000 different shades of green.

And then there are full-moon swims at the end of lazy, hazy summer days. Under the moonlight, when you put your hands in the water, it kind of curves above them like mercury. It’s a magical time to be in the water. Dusk is quite noisy, with all the birds settling down, but the river is still and silent when it’s dark. But I love autumn river swims most of all, perhaps because I love that season the most. I love the colours, and how the air smells damp and earthy.

Whenever you pass someone on the bank, all anyone ever says to you is: “Is it cold in there?” They say it all the time, particularly the fishermen. I think that’s the British obsession with the weather.

You must get in with intention — that’s the important thing with outdoor swimming. Don’t just stand there dipping your toes in, wondering if it’s warm enough, because if it’s in Britain, chances are it won’t be. Then, once you’re in, exhale. In 90 seconds’ time you will find your circulation’s kicked in, your skin will be nice and tingly, you’ll be charged up. Getting in is always worth it.

Breaststroke is the best stroke, because you actually want to see around you and look at the clouds. But I do love crawl. Physically it’s a beautiful motion, because you are all stretched out and you’ve got water streaming all the way down the sides of your body. I’m not so much of an exhibitionist that I’m desperate to go skinny-dipping — although obviously it can have its place — and I feel quite restricted in a one-piece, so I wear a bikini.

Swimming has returned me to a lot of the joy I used to have in my childhood. I had a fairly feral childhood in some ways, running around on a farm, and that sense of freedom is hard to duplicate. Swimming is the only thing that makes me feel really calm and liberated at the same time. I am someone who tends to feel things very intensely, so although the joys of life are readily available, its pains are too — and swimming somehow helps reset the body clock to some sort of base level.

Interview: Danny Danziger. Photographs: Emma Critchley

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