More than 250 people withstood sub-zero temperatures in the early hours for a winter solstice dip in the lake.

Marking the shortest day and longest night of the year, young and old left their swimmers and insecurities on the sand to take part in the annual Lifeline fundraiser.

The sound of bagpipes playing on the bay was replaced with squeals of shock and - assumedly - delight as the group tiptoed into the water.

Taking the plunge for the first time, Elna Jennings described the experience as "exhilarating".

"It was ice cold but that's alright, I don't mind the cold," she said.

"I'm a triathlete so this is my open water swim for the day."

The Indigenous Marathon Foundation employee said the foundation celebrates resilience and this was her way of supporting their mission.

The Watson resident moved from South Africa three years ago. She said several close family members back home struggle with depression and anxiety.

"I'm really doing this for everyone I love and for myself as well, for renewal," Ms Jennings said.

"I'm going through some things too but I celebrate life despite of it."

Ian Lindeman started the swim in 2017 to raise money for charities in the fight against mental illness. He had battled cancer and sadly died in November, 2019, aged 70.

Organiser Ben Johnston said greater awareness of the event had led to a surge in participation since the inaugural event.

"We went from four to about 50 to then 150 to then back to two last year because of Covid and then up to 250," Mr Johnston said.

"I think we can probably get up to about 400 here at Yarralumla Bay before we have to find a new site."

Winter solstice swims also took place in Tasmania on Monday and on Antarctica's Macquarie Island.

Expeditioners at Australia's three research stations honoured tradition and celebrated the year's shortest day and longest night by taking a dip in sea ice or the ocean.

In Hobart, daytime is six hours and 21 minutes shorter on the winter solstice compared to the summer solstice, while in Canberra it is four hours and 46 minutes shorter.

The solstice will also spell the start of a week of wet weather for Canberra, with rain forecast from Wednesday through to Saturday.

Temperatures are unlikely to go above 12 degrees on Friday and Saturday with wild weather forecast on the mountains towards the end of the week. Perisher predicted more snowfall for the weekend.

Fundraising will remain open on the Winter Solstice Nude Charity Swim website until June 30.

Bare Breaststrokers was ahead on the fundraising leaderboard on Monday with more than $2800 raised so far.

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