Andy Donaldson and his team were aware of the dangers that lay ahead, but just in case a reminder was needed, a huge 2.5-metre freshwater crocodile waiting at the start ramp ahead of his longest ever solo swim put the challenge into stark focus.

Donaldson, a British-Australian ultramarathon swimmer, was about to embark on the 55km Dam to Dam Challenge from Lake Argyle to Kununurra in the East Kimberley, hoping to become the first man to complete the gruelling endurance swim.

Adding to the difficulty was the fact the Ord River in remote Western Australia is well known for its reptilian inhabitants; the freshwater crocodile population numbers 5,500 – one croc for every 10 metres of his swim.

Fortunately for the 35-year-old, freshwater crocodiles are smaller and more timid than their saltwater counterparts – the world’s largest reptiles – and unlikely to approach humans.

Donaldson’s team had done its research beforehand and he never felt threatened by the wildlife surrounding him, which also included eagles, ospreys, kits, cormorants, darters, turtles and big catfish.

“It was a bit nerve-racking doing a swim in the open water,” Donaldson said. “There’s always a risk of wildlife. But in the same breath, people use that river every day recreationally.

“They say ‘fear is a mile wide and an inch deep’ – the perceived fear is a lot bigger than it actually turns out to be.

“There’s always a bit of a rush with adrenaline if you see anything when you’re in there or if you touch some seagrass or anything, but I didn’t actually see anything during the swim at all. It was a largely by-the-book swim.

“As always, safety comes first. We’re not putting ourselves intentionally in harm’s way. If there is anything that looks threatening, we pull the pin because we want to be smart and we want to use these challenges to share positive messages, not negativity and fear.”

Having successfully navigated the course, finishing in front of hundreds of people lining the banks of the river in Kununurra, he posted a record time of 11 hours and 51 minutes, bettering the mark set by Simone Blaser, who was the first person to complete the swim with a time of 16 hours and 13 minutes in 2024 – and was part of Donaldson’s support crew on Tuesday.

Donaldson said he was “over the moon” to complete the swim.

“It was just magical – swimming through these ancient gorges, the red cliffs, the sunrise was just spectacular out there,” he said.

“I’ve had the opportunity to swim in amazing places all around the world, like Hawaii, Greece and Croatia. But I would have to say, hands down, this is the best swim I’ve ever done. It’s the most beautiful place for swimming I’ve ever experienced. It was just incredible.”

Starting in darkness at 5.38am, Donaldson was able to set a good pace in the early hours of his swim, until the searing Kimberley sun pushed the mercury as high as 34C and prompted support boats to try to provide shade for him.

A lack of salt – and therefore reduced buoyancy – in the freshwater complicated matters further.

“Especially when you start to fatigue, your hips drop and your body position isn’t as good, so you feel like you’re dragging the legs a lot more,” he said.

An unexpected headwind and a section of “dead water” – where there is no current – made things even trickier, but with the support of his sizeable team he made it to Swim Beach, 6km from the township of Kununurra, by 5.29pm.

As he neared the finish line, local swimmers joined him in the water for the last 200 metres.

“These challenges, they’re never achieved alone,” he said. “You always have a skipper, a paddler and your coach out there in the water, people that know the river systems well so that you’re in safe hands, you can navigate those challenging sections.

“The team, the energy and the encouragement pick you up when you start to falter. These marathons are similar to the marathons of life where, if you want to pursue something, a dream, or go after big goals, you can go a lot further when you have great people around you.”

The Scotland-born, Perth-based athlete is considered one of the world’s leading ultramarathon swimmers. He holds a number of world records and in 2023 became the first person to complete the notorious Oceans Seven marathon swim challenge – comprising seven ocean channel swims – in a single year.