Andy Donaldson will swim the upper Ord River, from Lake Argyle to Kununurra's Diversion Dam, in Western Australia's remote Kimberley region, on Tuesday - a distance of 55km.
He is aiming to break the record set by the only other swimmer to attempt the epic feat, Simone Blaser, who completed the journey in 16 hours and 13 minutes in 2024.
Mr Donaldson is convinced he can smash Ms Blaser's mark.
"If it was current-neutral, I'd be looking at 12 hours, perhaps 13 hours," he told AAP.
"But we might get a bit of a push. There's been a lot of rainfall over the wet season, so the currents I think will help us.
"I'd like to put a challenge out there to go under 10 hours."
Mr Donaldson has a swag of world records to his name, including the 45km Manhattan Island circumnavigation, the 170km Bahrain Swim Challenge and the 104km Ibiza Swim Challenge.Â
The upper Ord River is inhabited by large numbers of freshwater crocodiles, which locals are accustomed to swimming with and are considered mostly harmless to humans.
However, a boom in dangerous saltwater crocs downstream on the lower Ord River has raised concerns in recent years.
Mr Donaldson - who will swim without a protective cage - said risk was part of the deal.
"I'm an open water swimmer. I've swum in a lot of waters with marine life," he said.
"The locals are jumping in almost every day and they've assured me the risk is minimal.
"Let's just say we don't want to be reckless."
Mr Donaldson, who grew up in Scotland before relocating to Australia in 2013 at the age of 22, pursued Olympic swimming earlier in his career.
When those dreams didn't pan out, he switched to open water competition with immediate success, winning the Rottnest Channel swim in 2021.
He said the format posed unique physical and mental challenges, and often involved swimming much further than assumed.
"You can be out there far longer than the distance as the crow flies," he said.
"If the winds are bad or if the currents and tides are pushing you in the wrong direction, you can be swimming an extra 10, 20, 30 kilometres."
Besides exhaustion, dangerous currents, hidden objects and encounters with marine life, physical risks associated with open water swimming include hypothermia and pulmonary oedema.
But Mr Donaldson is a sucker for punishment.
"You need to connect with the 'why', because it's the jet fuel that powers you to push on when things get tough," he said.
And that, he says, is a metaphor for why he does it.
"I like to use the swim challenge as platforms to inspire others, to share positive messages around what people are capable of, how to handle adversity and thrive and grow from it," he said.
Previous swims have raised funds for mental health charities including the Black Dog Institute and the Kai-Fella foundation, for which he is an ambassador.
The World Open Water Swimming Association will ratify Mr Donaldson's Ord River attempt.
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