A heartfelt letter penned by an Australian swimmer to his childhood coach reveals the moment an Olympic flame was lit inside him.

When Jack Cartwright lines up on the blocks at the Paris Olympic Games next month, a dream inspired by the swimming trainer will be realised.

"It really is a dream come true," Cartwright said from the team's pre-Olympic training camp in the French Riviera this week.

But he had to work harder for it than most.

He started his swimming career in his small country hometown, Biloela, in central Queensland, but he quickly outperformed the level of training available there.

While kids in the city or bigger regional centres spent a few minutes in the car each day, Cartwright and his three older brothers, Henry, Sam, and Rob, made the three-hour round trip to Gladstone every afternoon, ferried by their mum, Michelle.

"It was never forced upon us, but Mum and Dad [Brad] always wanted us to do a sport to make friends and get involved in our small community," Cartwright said.

In addition to family support, Cartwright also had a special bond with his childhood coach, Caroline Hayes.

"You will be a big part of me when I hurdle through my swimming career," a young Cartwright wrote to her in 2013.

"As you were the one that motivated me and made me feel like swimming would always be the sport I will be competing in."

The now 25-year-old choked up when the note was read to him this week.

"That's amazing … it's all true," he said.

On reflection, Cartwright said his Olympic dream was ignited from that moment.

"Caroline was just a wonderful coach and wonderful guidance to have her in my life," Cartwright said.

Clocking up the kilometres in the family car on road trips – and in the pool – across the state for swimming carnivals became a way of life Cartwright embraced and loved from a young age.

"I guess the grind itself as a swimmer, you don't really know anything else, and I put all my attention into swimming and following that black line," he said.

"Growing up, it was such an awesome feeling when you're doing PBs [personal best times], and you're smashing times left, right and centre at meets, and you just want to keep going."

Ms Hayes said this dedication made Cartwright destined to one day realise his dreams of swimming for gold at the Olympics.

"Jack was always a very dedicated swimmer and had the wonderful support of his family," the retired coach said from her hobby farm in central Queensland.

Ms Hayes said Cartwright's letter was one of her "special keepsakes" from her decades as a swimming coach.

She said she had supported Cartwright's blossoming career after he moved to Brisbane to attend boarding school and chase his Olympic dream.

"I was absolutely over the moon when he made the [Australian Olympic] team … it's so well-deserved," she said.

Cartwright said it would also be a proud moment for him when his parents, Brad and Michelle, watch him represent his country at his first Olympics.

"It's going to be so special," he said.

"It just means the world to me that they are able to travel the world with me and experience what I get to experience."

He may not be a household name like Australian teammates Ariarne Titmus and Kyle Chalmers, but the "boy from Biloela" can claim to be his hometown's most famous sporting product since Test cricket wicketkeeper Ian Healy.

Currently training in Canet, France, the Dolphins team features many strong medal chances, including Titmus, Chalmers, Emma McKeon, Mollie O'Callaghan, Kaylee McKeown and Zac Stubblety-Cook.

Cartwright is one of 22 Dolphins who will make their Olympic debut when the swimming program begins on July 27 in Paris.

The freestyle speed machine is a member of Australia's reigning world champion men's 4x100 metres relay team gunning for Olympic gold.

And Cartwright is well aware that if he wins, it will be a win for not only his nation but also the country town and its residents who raised him. 

"It's a shared journey and lots of Ks [kilometres] on the road and in the pool."