Marathon ocean swimming is an endurance sport challenge unlike others. It takes patience and acceptance of discomfort and pain yet also faces unpredictable possible failure against the challenges of nature due to waves, wind, tides, cold, jellyfish, and sharks!

Australian marathon swimmer and entrepreneur Mark Sowerby’s story is shown in the 2026 feature-length documentary film directed and filmed by Jeff Tseng. The film narrates Sowerby’s successful attempt of the ‘Oceans Seven’ – seven of the world’s most challenging open water swims. Likened to climbing the 7 highest mountains, this is a challenge Sowerby pursued across five continents and a decade of swimming. The film is entertaining and includes beautiful seascapes. However, it most significantly offers deep lessons of personal growth.

Sowerby had been highly driven in work as a venture capitalist. When his business struggled and his integrity and ethics were challenged, he lost his zest for life and went into a deep hole of a mental health crisis including suicidal ideation. Swimming was an outlet and the Oceans Seven challenge became a therapeutic journey. Like some other age group endurance athletes, he was perhaps exchanging one driven obsession with another. Nevertheless, on the journey he learned much about himself and resilience.

What most interested me was Sowerby’s conversation with Hawaiian-based shark and jellyfish expert Dr Angel Yanagihara. She warned Sowerby there will be sharks on his swims, but he should remember to keep his heart rate down, keep his breath and stroke rate calm, avoid splashing, and thus not send out messages other than that he belongs there as another big swimmer. This conversation inspired the movie’s title ‘Don’t Be Prey’ and the implication ‘Don’t be a victim’ to his other life challenges.

The film follows the Ocean 7’s journey from the English Channel through the longest 42km Molokai swim in Hawaii, the darkest overnight swim of Catalina, the team of 4 swim across the Strait of Gibraltar, the coldest across the North Channel, the paired swim across the Cook Strait in Aotearoa New Zealand and, perhaps the toughest, across Japan’s Tsugaru Strait.

He completed the swims on June 29, 2024 at the age of 52. He was the 29^th person to achieve this milestone of now 44. He leaned on the coaching of Tim Denyer, the companionship of his wife Heidi, and the motivation of inspiring his two sons.

He had different mantras to confront inevitable psychological battles at different stages:

‘The only thing that is going to stop you swimming across the channel is you.’

‘I can’t do anything that’s difficult at less than 100%.’

‘This sport is binary – 0 or 1 – you get over or not.’

‘One day to change your life.’

‘It’s not about me.’

‘Training is the hard part. The swim is the celebration.’

‘Train for the worst. Hope for the best. Accept what you get.’

The film demonstrates both the physical and mental challenge of marathon swimming. Its lessons for disciplined preparation and planning for audacious goals, for confronting and overcoming fear and despair, and for pursuing individual achievement in community with others are inspiring for other open water swimmers and endurance athletes. Yet there is also inspiration for anyone facing their own challenges.

‘Don’t Be Prey’ is a movie and concept that I look forward to watching and discussing with soldiers. I highly recommend it as a great yarn of a documentary with many lessons to adopt for Defence members.

For an overview watch the official trailer.