The Mackerels began as a mens-only adult winter swim club 51 years ago but now has women and children as an integral part of the club. Swimmers are arranged into heats and a staggered start system means any participant can potentially win their race.

President Steven Weller said this year's launch had attracted record numbers for the club, with 22 new swimmers and 68 people in total. Women made up about 50 per cent of attendees.

The youngest people jumping off the diving blocks today were 10-year-olds Billie Eder, whose mum Janey Eder is a competitive Mackerels swimmer, and Kobe Weiner.

Kobe has been coming for winter swims with his pop since he was six. The keen competitor took a short break following an interstate move last year but is pleased to be back in action.

"It's good to get out of the house and do something," Kobe said before running to the starting blocks for his heat.

Kobe is known by many at the club. He said he has met "heaps" of people who encourage his swimming.

The Mackerels is a family affair for many. The oldest member, 84-year-old Brian Schrader has been with the club for 34 years. He now brings his adult 31-year-old granddaughter, Jasmine Turvey, each week.

Ms Turvey has been swimming with the Mackerels every weekend of the season for a year and said it felt like a legacy to her grandmother, who taught her to love the water.

"I know this is really important to [my pop]," she said. "I come to spend time with him."

Ms Turvey previously swam with her pop at Newcastle Diggers Swimming Club before moving over to the Mackerels. She has now convinced several of her own friends to join and wants to see other young swimmers at the Sunday meets.

"It's such a nice way to spend winter mornings," she said. "It's a good way to start your day. You feel very accomplished."

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Despite the club's male history, Ms Turvey said she felt women were integral to the Mackerels. Most winter swim clubs in the area now encourage women and kids to join and have seen growing female participation rates over the last 15 years. Ms Turvey would like to see all clubs take this up.

For Mr Schrader, this growth has meant more people to share the water with. He swims everyday but enjoys the turnout of a winter Sunday morning.

"I like the friendship. We all like to swim," he said. "It's great to have the biggest event in a long while."

Swimmers were not short on entertainment for the launch. The baths were christened with blocks of ice - a Mackerels tradition. Dry ice is usually used to create steam though none could be sourced this year.

A pipe-band from the City of Newcastle RSL led competitors to their starting blocks before the first heat plunged into the salt water. Swimmers enjoyed cups of soup to warm up after their heats.

But for some, today's swim was a mild one. Mr Weller was surprised by the conditions so far into autumn.

"The water temperature was 21 degrees, which is really warm," president Mr Weller said. "It will get down to 14 or 15 degrees through winter."