The epic experience for this year's Simpson Desert Ultra meant competitors had to deal with flooding and rain.

"Flooding in June - that's nearly unheard of," race organiser Jenna Brook said. "Dad said to me at the start of the week, the river's rising at Durrie, but none of us, police or emergency services, thought it would be high enough to stop traffic."

But that's what the Diamantina River did last week, fluctuating in height from 0.35m to 1m, gradually cutting access to Birdsville for contestants driving from as far away as NSW and Victoria.

Working with police and utilising the resources of locals, the SDU team managed to ferry across everyone who arrived on the eastern side of the river and found they couldn't cross.

Flatbed trucks were called in to help, along with a Unimog that was in town.

"People were making phone calls to me, to the police, leaving us messages on the Facebook page," Jenna said.

One of those who arrived after the last trip across the river on Friday afternoon was Chelsea Holton, who had been driving with three companions from Canberra since Wednesday.

"By the time we heard the news of the 1200km detour via Winton and Boulia, it was too late, we would have missed the race," she said.

They kept heading west from Windorah, arriving to find the river was 75cm at its deepest.

Not having their car set up for camping, they decided that walking across was preferable to sleeping in their car, so they stripped down to their undies, packed their race gear in duffel bags and waded the 2km to accommodation in town with arms linked for safety.

"I never thought I'd be telling people I walked down the street in Birdsville in my underwear," Chelsea said.

Others spent the night in their cars at Birdsville racetrack, similarly unequipped for camping, but a call to the manager at Pandie Pandie Station saw them make an emergency 30km dash north to deliver blankets for warmth.

Overcast conditions early in the week gave way to mist on Thursday and light rain on Friday, as organisers were setting the course and race hub up.

"The course was slippery but the sand was wonderfully compact, compared to last year," Jenna said.

"It was a difficult course even then, and people gave themselves more time to complete it this year.

"Everyone said it was brutal but wonderful."

Chelsea Holton was back for a second attempt this year after stopping at the 75km mark last year and, using walking poles to provide more contact points with the ground in the slippery conditions, punched out the whole 100km course this year.

Posting on social media, Kathy McGregor related her determination: "Four sleeping in the Grand Jerokee Friday night stranded at the racecourse , then getting the unimog across at 10am not great prep before heading out to hub at 1pm to start at 2 to complete the 100km.... We all did it!!"

All up, Jenna said 132 people were able to make it to the starting line, with between 20 and 25 unable to get to Birdsville or not willing to leave their cars unattended.

After the ultra trail marathon was over, around 70 people had to be returned back to the eastern side of the Diamantina, by the SES flood boat, and 20 vehicles were transported across on the back of flatbed trucks.

Rather than repeating her wading effort, Chelsea took the boat, but that wasn't the end of the adventure.

Knowing the Diamantina had broken out across the road 15km east of Birdsville, Jenna had armed returning runners with aerial shots of the area that showed a route around the flooding there.

"We walked around and found a safe route and were able to drive around it and keep going," she said.

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