Tingling and buzzing - what's the point of ocean water swimming in the middle of winter?

It's just shy of five degrees in Wellington - but a balmy 10 in Seatoun Harbour - where a group of about a dozen hardy women prepare to wade in.

There's no splashing, dashing, whooping, hollering, or shouts of "shit, it's cold" as you might expect.

The sun rises beyond the hills casting a beautiful glow across the gently rippling water. The Better Beach Babes strip down to their togs and beanies and ease themselves in, taking deep breaths to allow their bodies to adjust to the cold.

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One of the group's founders, Adrienne Linney, has some survival advice for this first-timer.

"You're gonna try and stay calm. When you first get in there, your body is gonna go 'what the hell is happening?', it's gonna be a real shock, and your heart rate is going up.

"If you just give it a minute, your heart rate will come right, and just do some deep breathing... just slowly ease your way in."

Linney has been swimming about three mornings a week for years and in 2020 started the Better Beach Babes inspired by a group of older swimmers she’d seen taking icy dips. Some mornings she manages to gather a group of 25 babes in Wellington, a few aged over 80. 

“There used to be a group of women who had a little bobbing group, they called themselves the OBEs, the Over Bloody Eighties. I remembered them from the early2000s, I used to walk past the beach and see them out there bobbing around and I thought they were crazy.”

They “always looked so happy, they just had a vibrancy to them, just a buzz”, she says.

Linney, who reckons she used to wear a wetsuit and “quite a wimp in the water”, now spruiks the mental health benefits of cold water swimming in the middle of winter.

“It’s like all the apps in your computer have shut down and you’re going back to the start again.

“When you’re in that moment with the cold and the nature and the beauty around you, there’s no space for all the other stuff going on in your life.”

On this particular morning, the babes spend about 15 minutes bobbing in the water.

"My hands are tingling now," one swimmer says.

"It's like there's a buzz," another adds.

Some days are harder than others, when the women are bashed by waves and covered in seaweed.

But even then: "There's not ever a day that you walk out of the water going, I wish I hadn't done that."

Further up the North Island, just before dawn on a chilly Wednesday morning at Lake Taupō, another brave group remove puffer jackets and wade into the cold water for a pre-work swim. This is the weekly ritual for the Dip and Sip club, who live by the tagline "you never regret a dip".

British expat Fleur Smith and her sister-in-law Phoebe Smith kicked off the “cold water social group” about a year ago, wanting to meet like-minded people who were keen for a “quick social fix” before work.

Fleur said the group wear beanies and bring hot water bottles to warm up before rewarding their tenacity with a hot drink at a local café afterwards.

Sometimes, they experience a beautiful sunrise and a glassy lake. Other days can be tougher.

“We found that rain isn’t actually the worst, because if it’s raining it’s actually warmer outside.

“If there’s waves and it’s windy then you have to get out, and you’ve got that cold wind coming off the mountains, that’s the worst.”

On these mornings, the numbers drop down to four or five. But throughout winter there are usually 15 – 20 swimmers willing to take the plunge.

“You do get the sense of accomplishment, you feel like you’ve already achieved something before you start your day,” Fleur said.

Entering cold water puts a big cardiovascular and respiratory stress on the body, explains Dr Jim Cotter, professor of exercise and environmental physiology at the University of Otago.

Cotter is a cold water swimmer who enjoys the frosty temperatures of the deep south.

Whether you swim in 2-degree water or 14-degree water, the impacts on the body are the same. Anything under 15-degrees is considered "cold swimming", he says.

“The reason is that your skin receptors cool down at a rate that it wouldn't matter even if it was 0-degrees. The skin doesn't send the information back to your brain any more powerfully than it would at 15-degrees.”

Performance and vitality specialist Jo Shortland runs a weekly cold water swimming group near an estuary in Raglan.

She says one of the biggest benefits is gaining control of our fight vs flight response.

“Fight/flight can be related to over-worrying or rumination, or kind of anxiety and stress response.

“Using the cold to calm that part of us by being very present, because when you are in super cold water you cannot be anywhere else other than in that moment.”

Cotter agrees.

“Just the effects of mastering the cold, the distraction effects associated with it, there may be some endocrine effects that directly change your brain function.”

However, he warns cold water is a “pretty powerful environment,” so “if you're middle-aged, before you jump into this type of thing, I would be checking out what your cardiovascular health is like”.