Perfect Swimming Temperature? 16 Degrees Centigrade. Here’s Why

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Water Temperature

It’s the first day of autumn in the northern hemisphere. That’s the official date, although in south London summer collapsed after a heatwave in June. But as any outdoor swimmer will tell you, clouds at the time of this year have a bright silver lining.

As the days shorten, so the temperature falls. Two weeks ago, swimmers at Brockwell Lido were bustling and bumping up and down the lanes in water temperatures of 23 C. Following a series of chilly nights, we’re back down to 16 degrees (60 degrees Fahrenheit). And it’s perfect.

Here’s why. At 16 degrees, the water begins to take on a life of its own. It becomes more viscous, or ‘syrupy’ in popular poolside parlance. Instead of slipping through thin liquid, your hands have something to grasp and there’s a real sense of pleasure as pull yourself through the water, head-butting the occasional leaf or two.

Cold water, hot showers

The pool itself is a lot quieter. We’re always at pains to make outdoor swimming as inclusive as possible, but there’s quiet satisfaction to be had when watching the fair-weather crowds fade away. (On that note, it’s worth pointing out that the number of winter swimmers, at least at Brockwell, has increased significantly since it started opening all year round in 2012).

Getting in is a whole new experience. Close to the equinox, the water is often warmer than the ambient air temperature. If you walk and shiver all the way to the deep end, as this swimmer does, diving in is actually a relief. And it’s still just about possible to have an outdoor shower (hot) once you get out.

Coffee tastes better too in the autumn months. As any cold-water swimmer will tell you, the rush of endorphins brought on by a chilly dip plays well with the caffeine kick from your flat white. Cake – another essential swimming ingredient – also works better in low temperatures. And who cares about calories when 15 minutes of shivering is the equivalent of an hour of exercise.

And then there’s the general coziness of it all. I know, I know, I’m skeptical of hygge too. But the closest you’ll get to the sensation in the UK is huddling around the outdoor pool benches with a group of friends, wrapped up in your winter fleeces. With a coffee in one hand and a chocolate flapjack in the other life feels perfect (no scented candles required).

An electric epitaph for summer

Finally, the light. If an early morning outdoor swim is your thing, you become highly sensitized to the angle of the sun on your face and in the waters day by day. Brockwell Lido is no exception. Turn around at the deep end at this time of year, and you come face-to-face with the sun rising over the trees in Brockwell Park.

As you swim back to the shallows, the light dances on the surface of the water, dizzy and dazzling. An electric epitaph to the passing of summer? Or a solar fanfare for autumn’s arrival? Both probably. 16 degrees centigrade. It really is the perfect temperature for outdoor swimming.

For anyone interested in the science, here’s a water viscosity chart courtesy of the wonderfully named Viscopedia

Water Temperature