By Steven McIntoshEntertainment reporter

Sharks, jellyfish stings, tropical storms, navigation problems and physical exhaustion are the kinds of issues that fortunately don't trouble the average person during a standard day at the office.

For retired athlete Diana Nyad, however, these were the very challenges she faced during the several attempts she made, in her early 60s, to become the first person to swim the 110 miles from Cuba to Florida without the use of a protective cage.

Most people, including Nyad herself, thought she had retired from competitive swimming at the age of 30. But more than three decades later, she decided to chase the goal that eluded her in her 20s.

Having previously attempted the swim in 1979, Nyad made four further attempts to cross the water from 2011, finally realising her dream in 2013.

Her story has now been adapted for the screen by Netflix - and could see actress Annette Bening score an Oscar nomination for playing the swimmer, who was supported on the journey by her friend and coach Bonnie Stoll.

"Every time you go out to do the swim, of course you think she's going to make it," the real-life Stoll tells BBC News.

"And it's a drag when you don't. Mostly for her, because that means another year of training, because she wasn't going to give up, no matter what."

Stoll is as much a part of the story as Nyad herself. Played by Jodie Foster in the movie, she sailed alongside her best friend, masterminding the operation and keeping the journey on course.

"I played racquetball for 10 years and Diana was my fitness coach, she taught me a lot about fitness," Stoll explains. "So for me to be able to turn it around and coach Diana in something was really cool, and I loved it. I learned more about the human will than anything else."

The film, titled simply Nyad, is the narrative debut for wife-and-husband directing duo Elizabeth Chai Vasarhelyi and Jimmy Chin. They have previously made documentaries such as Free Solo, about a vertical rock climber, and The Rescue, about the boys who got stuck in a cave in Thailand.

"Like moths to a flame, Jimmy and I are attracted to these stories about individuals who push the limits of possibility," Vasarhelyi explains. "And Diana Nyad is just that.

"The Rescue and Free Solo had been centred around a man or group of men. And for a while we had been looking for - how does that will manifest itself in a woman? What does it look like, how is it different?"

Who is Diana Nyad?

• The long-distance swimmer shot to fame in 1975 when she swam around Manhattan
• In 1979, she swam 102 miles from Bimini, Bahamas, to Florida in 27.5 hours, setting a record for distance swimming over open water
• She retired from competitive swimming aged 30 and spent the next three decades as a sports broadcaster
• In 2011, she came out of retirement to attempt to become the first person to swim from Cuba to Key West, Florida, without a shark cage
• It took her three further attempts over three years, but she finally completed the feat in 2013 aged 64, following an excruciating 53-hour swim
• But she has been a divisive figure among endurance swimmers, with controversy around some of her claims

Usually in films, anyone other than the main character is referred to as a supporting character - and the person playing them a supporting actor.

Never has that been a more appropriate title than in the case of Stoll - who was the ultimate support to Nyad, year after year, as she continued to sail alongside her friend as she went after her goal.

"I was the supporting role," Stoll concurs. "In her head, we did it together. In my head, I watched her do it.

"For the years of the attempts and training, Diana and I were on the exact same page," she recalls. "We can bicker, but I don't think we bickered once [during that time]. I roll my eyes a lot, but for those years I didn't roll my eyes."

One of the most interesting aspects of the film is how Nyad overcomes the dangers. Sharks, for example, are deterred thanks to a piercing audio signal being sent from the boat.

Nyad was, however, stung by a box jellyfish on her forearm and neck, causing severe respiratory distress and putting paid to her third attempt. For her next swim, she wore a custom-made protective mask.

Her eventual success in 2013 was so extraordinary that some critics raised doubts. Did she really not hold on to the boat at any point to rest her body? Could she really have made it unaided in such a short time?

The World Open Water Swimming Association said there was a "significant gap" in the records for her successful swim, and it has not been officially ratified. Guinness World Records also rescinded its recognition.

Separately, Nyad had previously been accused of exaggerating or making misleading statements about previous swims, and has been described as "a self-aggrandising scourge of the marathon swimming community".

But her team attributed her achievement to the fast-moving Gulf Stream flowing in her favour, and Nyad rejected the queries by saying: "I swam. We made it, our team, from the rocks of Cuba to the beach of Florida, in squeaky-clean, ethical fashion."

The Marathon Swimmers Federation also backed Nyad and said there's no evidence that she cheated.

Stoll provided food and liquids to Nyad from the boat. She was assisted by helpers including chief navigator John Bartlett (played by Rhys Ifans in the film).

"No sarcasm was one of the rules," Stoll recalls. "And not telling her what time it is. But it was a team, for sure. If everybody does their job the way it's supposed to be done, it's going to be successful."

The film has broadly gone down well with critics, many of whom praised Bening's portrayal of an unapologetically headstrong figure.

"Bening is the best she has ever been as Nyad, embracing the athlete's stubbornness and strong will to a tee," wrote Isabella Soares of Collider.

"Kudos to [screenwriter Julia] Cox and the entire team for never shying away from the rougher aspects of Diana's personality for the sake of 'likability'," added Maureen Lee Lenker of Entertainment Weekly.

But speaking about the film more widely, she added: "Nyad simply tries to do too much. Each attempt at the swim should play like a thriller, the stakes of the moment a breathless sequence, but this is undercut by the pacing challenges in other areas."

Nyad herself has told the LA Times she was "blown away" by the film but that she wasn't able to talk about it any more because she's part of the US actors' union, whose members are currently on strike.

Stoll says the movie is "very" true to life. "There is more to Diana's personality because it's so diverse, but the film is who she is, in every way," she adds.

Nyad is a tough character to like, and the depiction of her in the film is not sanitised. "It was important to create a full picture. You never see roles like that for women," Vasarhelyi explains.

It's not hard to imagine Bening scoring a fifth Oscar nomination for the wide-ranging role. "I mean, Inshallah, right? God willing," says Vasarhelyi.

The best actress race is crowded this year - with likely competition from Emma Stone, Carey Mulligan, Lily Gladstone and Sandra Hüller among others.

"I don't know, I think awards are magic, but I will say [Bening's] performance is certainly worthy of great recognition," the co-director reflects.

"She trained for over a year, she didn't hesitate to play a complicated character you may not like all the time. And I was incredibly impressed by how she inhabits her body at 64."

Nyad is released in cinemas on Friday and on Netflix from 3 November.

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