02/07/2015 13:33 BST | Updated 02/07/2016 06:59 BST

In Praise of Year-Round Outdoor Swimming

Yesterday a dowdy brown duck swam across my path, leading eight fluffy black and yellow ducklings no bigger than golf balls. They were only inches from my nose but barely glanced at me. The day before, when two cormorants lurked, the ducklings hid among the wild irises at the water's edge, so I am obviously less scary than a foot-tall black seabird. As a city dweller, I get a back-to-nature buzz from outdoor swimming in summer that's sadly lacking in chlorinated council pools. There's no better way to cool down and freshen up on a sticky, sweltering afternoon, but I'm also a huge advocate of swimming outdoors all year round, even when the snow is lying. It's transformed my life in all kinds of unexpected ways, and could do the same for you.

I started swimming at the Hampstead Heath women's pond in 1996 and loved the sparkly summer evenings spent there, but used to give up when the mercury dipped below 12 degrees C. This was around the time the clocks went back at the end of October and it was with gloom that I returned to the tedium of swimming lengths at the local gym. A few hardy women continued at the pond so one year I decided to see how low I could go and thus transformed into a born-again winter swimmer. It was easy. Honest! If you swim regularly two or three times a week you become acclimatised - but being an addictive personality type I soon found I couldn't miss a day. Perversely, I even looked forward to the most extreme cold when the water tingles with ice crystals. And here's why:

• You grin from ear to ear when you swim in water less than five degrees C. My partner thinks it's because I'm glad not to have died - and yes, cold water shock can be fatal. But in fact the grinning is caused by a cocktail of endorphins and other happy brain chemicals that flood your veins and boost your mood for the rest of the day.

• You have Technicolour skin when you climb out of the water: lobster pink and mauve in my case. The circulation boost has great anti-ageing effects on the capillaries, leaving skin supple and glowing. Some claim it combats cellulite as well.

• You burn more calories in cold water than warm because your body has to work harder to keep the internal organs functioning. So you can eat more without putting on weight (within reason).

• It's years since I've had a cold or flu - those pesky bugs don't seem to survive daily immersion in freezing water. A Czech study has found the white blood cells that fight infection become more reactive in regular winter swimmers, so that could explain it.

• Winter swimming lowers the cortisol levels in the blood, which makes you feel less stressed, and long-term it also helps to improve the mechanisms by which you process sugar, making you less likely to get diabetes. And it boosts oestrogen levels in women and testosterone in men, which can make you feel more frisky in the bedroom department.

• Swimming is a gentle form of aerobic exercise, so you get a decent heart-lung workout - so long as you don't just pootle along chatting to a swim buddy. Outdoor swimming is very sociable, like joining a secret club of people who are all slightly bonkers in the best possible way.

• I'm a novelist, and if I'm stuck for the solution to a plot problem, it usually comes to me by the second or third circuit.

So what are the downsides? All my non-winter-swimming friends think I'm a loony, but I can live with that. On grey, blustery days it can be hard to raise the motivation; I just have to remind myself how great I'll feel afterwards. If I don't take enough extra layers I get shivery on the way home and it can take a while to warm up again. And if you have high blood pressure or a heart condition, seek medical advice first because it may not work for you.

Winter swimming is not for everyone - thank goodness, because I don't want my pond to get any more crowded than it already is. Some of the most special moments are when I have it to myself. There's a place down near the end where a tree overhangs the water and sunbeams dance and when I float there, at that precise moment all is right with the world.

Gill Paul's latest novel No Place for a Lady, about two Victorian sisters caught up in the Crimean War, is out in paperback and in ebook