Competitors say they both love and hate Darwin's gruelling Kamfari bike race.

The annual quad and motorbike Kamfari is as much a race as it is endurance event.

Conditions were so challenging on Sunday afternoon that nearly half the competitors dropped out before finishing the full race.

At the sound of the starter's rifle, the bikes take off for loops around a 12-kilometre track, while the quads head off to another one.

Within a minute, this year's 49 motorbikes and 28 quads were all in deep, Top End water.

Low rainfall over the week had organisers worried, but rain overnight into Sunday helped top up the swamps and bogs.

A total of 49 motorbikes and 28 quads raced around two 12km courses. ( ABC News: Jacqueline Breen )

'Just get out there and be insane'

After pushing through the most water-logged laps in four hours, winner Brad 'Wonka' Williscroft said this year's race had been one of the hardest.

"When you're out there you're like 'speak for yourself, what am I doing out here?'" he said.

"It's tough work. But when you get the win, it's worth it."

Spectators have to be willing to cop a spray for a front-row view. ( ABC News: Jacqueline Breen )

Quad-biker Michelle said she hoped to cross the finish line, and said racing helped her "de-stress" from work.

"I used to be pretty mellow, I wouldn't do mad things and all of a sudden [I decided] I was going to just get out there and be insane," she said.

Willis-Croft's win brings his total to 10 Kamfari championships, equalling the current record.

But he said it might be his last.

"These young blokes are getting faster, and my goal was to equal [the record]," he said.

"I've never been beaten so I don't know if I'll come back again do 11 or just stay undefeated."