Several people were treated for minor injuries after spending up to an hour in the water near Kununurra.

The fast-flowing water is frequented by crocodiles but none were spotted at the scene of the accident.

One of the seven, Helen Fitzsimons, said two boats collided tipping one over before the boat carrying the team from Orange arrived.

In their efforts to avoid the boats they ran into reeds which tipped their boat over plunging them into the water.

“I bobbed up under the boat, in the gap between the seats,” she said.

She said she and another Orange woman ducked down and swam clear of the boat before it sank.

“It was very scary, a few people were a bit shaken,” she said.

“It was certainly an adventure.”

She said people lost mobile phones, cameras, seats, paddles and other items in the incident.

“One of my shoes was sucked off when [the boat] toppled over.”

Mrs Fitzsimons said a rescue boat picked up crew from the first boat but there was not enough room for people from the second boat so they had to swim to the shore and sandbanks before they could attempt to re-float the boats.

VIDEO: The Ord River Marathon

Ord River Marathon co-ordinator Glenn Taylor said it was the first time in the event’s history that boats had capsized.

He said some of the people were treated for “minor bruises and bumps” by two ambulance officers who were travelling on a support boat.

“We’re very happy that everyone was safe,” he said.

“About 10 kilometres down the river there is a series of shallow water sections,” he said.

“They were a bit slow through that section and we think they may been little under-powered and they lost their bouyancy.”

Mr Taylor said the river was fed by a hydro scheme but he said the speed of the water was not as fast as rapids.

He said with the temperature at 34 degrees the water was reasonably warm and there was no risk of hypothermia.

Mr Taylor said there were freshwater crocodiles in the river area and there was the occasional saltwater crocodile.

“It’s the Top End, there could be crocodiles anywhere,” he said.

The event is 55 kilometres long.