Nyad true story: How the inspirational achievement was adapted for the screen

Nyad chronicles the swimmer's gruelling training, the mental challenges, and the physical setbacks – including a brush with a potentially deadly box jellyfish – that she endured to achieve her goal, as well as her enduring friendship with coach Bonnie Stoll (Jodie Foster).

Despite her absurd feat, some doubts have been cast over the authenticity of Nyad's claims, partly due to a sudden surge in her speed around 31 hours into the swim.

However, she and her team have always insisted that it was achieved in "squeaky-clean, ethical fashion".

And, indeed, The Marathon Swimmers Federation have also backed Nyad and said that there is no evidence of cheating during the Cuba swim.

So, ahead of release, RadioTimes.com spoke exclusively to Stoll and one of the film's directors, Elizabeth Chai Vasarhelyi, about adapting the story for the screen.

Nyad true story

In the past, Vasarhelyi and her co-director and husband Jimmy Chin have focused chiefly on documentary filmmaking – with Free Solo and The Rescue among their more well-known works.

But she explained that when they got the script for this film – adapted by Julia Cox from Nyad's own book Find a Way – they both instantly felt it was time to move into narrative dramatic features.

"Jimmy and I love stories about people who push the boundaries of what's possible," she explained. "And when we read the script for Nyad, we both had this moment of being like, Diana Nyad is just that.

"And it is a very unique opportunity to create two rich role roles for some spectacular female actresses. So I think it was that, and I think also we've made a lot of docs, and I was curious about how telling a true story would translate into narrative fiction. It's always nice to find yourself evolving creatively, and this was an opportunity to do that."

For Stoll, watching the film wasn't too far away from the experience of watching a documentary, and she explained that Vasarhelyi and Chin were scrupulous when it came to recreating real-life scenes.

"I'm really lucky to have every single person that was affiliated with this film," she said. "It's just really well done. And it's very true to life – seeing it on the big screen looked very real, very real."

She pinpoints one scene in particular – when Diana has been pulled out of the water and is close to death during one of her failed attempts – as being especially close to the real thing, while later she adds that a scene in which she and Diana celebrate the failed attempt of a younger swimmer also matches up with reality.

"We were pretty happy," she smiled. "That was really well done, because that's kind of what happened, except there were 10 of us jumping!"

As for seeing herself played by a two-time Oscar winner in Jodie Foster, Stoll said that she ended up finding out things about herself that she had never been aware of before.

"We spent quite a bit of time together," she said. "And she picked up a lot more than I realised until I watched the movie.

"I was telling Chai that, you know, I was sitting there watching, and then I see I was sitting there just like this, and I saw Jodie do it and said, 'Oh, maybe I do that a lot.' And then I saw her do it again. So I guess that's something I do. Which I didn't know!"

Although it might resemble a documentary in some senses – and the directors were after a strong sense of realism – Vasarhelyi explained that the process was rather different from putting together a doc and allowed them more room to experiment.

In particular, she was interested in finding ways to dramatise certain aspects of the story without them becoming too "monotonous".

"I was thinking more about, like, how do you dramatise the endurance of it?" she said. "How do we make the water and each swim build upon one another? How do we add meaning to that? You know, what is the function of memory here?

"And so it was very different as a process in terms of your prep, and it was also interesting to work with visual effects, where I've never had that opportunity to just create something."

The most striking use of visual effects in the film comes when Diana experiences some hallucinations underwater, after she has become delirious during the swim, which includes the yellow brick road from The Wizard of Oz.

And although this part of the film might sound less realistic, this, too, is very much based on Nyad's account.

"Those two hallucinations are based on real hallucinations Diana Nyad had," Vasarhelyi explained.

"But for us, they function also as a moment of levity and humour, trying to remind audiences of the delight that Diana does experience, the wonder, as well as how separate from her own body she becomes and how much she needs Bonnie, who's standing by her and her team because they really end up like being responsible for her."

One member of the team who is especially prominent in the film is John Bartlett – played by Rhys Ifans – the chief navigator who sadly passed away shortly after Diana succeeded in her fifth attempt.

The film is dedicated to his memory, something Stoll found emotional.

"Diana and John Bartlett were very close," she said. "Very close. And he was a great human being. I mean, nobody knows the Gulf Stream like he does – every 15 minutes he was pinging all along, because not many people know about the eddies. And when you're swimming two miles an hour and the boat has to go two miles an hour, it is not easy."

And she added that it was important to pay tribute to all the members of Diana's 40-strong team, even if not all of them could be prominent characters in the film.

"Everybody did their job," she said. "The shark divers, and then the boat drivers. And then, you know, they go on their mother ships to eat and sleep before they come back for their next stint."

Ultimately, though, it's Bonnie who emerges as Diana's true right-hand woman, and the film presents their friendship as a special and strong one.

Stoll said that she doesn't "think there's many friendships like this", and for Vasarhelyi, capturing this accurately was every bit as vital as ensuring authenticity in terms of the swim.

"It was incredibly important to us to kind of honour this idea of chosen family, and, like, a friendship between women of a certain age," she said.

"Because the film is not about a swim, right? The swim is a vehicle for exploring what drives this ambition in this complicated, complex woman, and then the kind of challenges she needs to work through to achieve her dream.

"And really, it's the friendship that emerges as kind of the beating heart of the film."

Nyad is now streaming on Netflix – Sign up for Netflix from £4.99 a month. Netflix is also available on Sky Glass and Virgin Media Stream.

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