A fatal quad bike incident at a Mid Canterbury river was “an absolute tragedy” but could have been “much worse” said a local who left the area that morning due to intensifying sea conditions.

A woman died in the water near the mouth of the Rakaia River on Saturday.

Police initially said the woman was swept into the water and died after she and others became stuck while attempting to cross on quad bikes.

Six people were rescued from the water and one of the survivors was rushed to hospital by the Westpac Rescue Helicopter in a critical condition.

The mouth of the Rakaia River is about 80km south of Christchurch. It is a popular spot with salmon and trout anglers, as well as boaties and 4WD and ATV enthusiasts.

The woman was out with a “small group” of people on quad and side-by-side bikes.

They were out individually - not as part of a tour or larger organised ride.

Ashburton councillor Russell Ellis had been in the area earlier in the day.

“I chose to come back because of the sea conditions,” he said.

“Other people decided they were going to go down there and continue fishing.”

Ellis said the group were not trying to cross the river mouth, as police initially reported.

“It’s a really unfortunate set of circumstances,” he said.

“They had been about 4km down the beach. About two-thirds of the way down there is a low area that you go through.

“Saturday happened to be particularly high seas coming through the low area.

“It caught these people and some others out. ”

Ellis said a local man raced to help, taking his truck down to try and pull the bikes to safety.

“He also got washed into the river,” he said.

“He wasn’t injured. Thankfully there happened to be a boat in the river fishing and they managed to attract the attention of that boatie and he came and rescued them.

“It could have been much worse. It’s just an absolute tragedy.”

Ellis did not want to criticise or blame anyone involved in the incident. But he said the tragedy was an opportunity to remind people about their safety in the area.

“Please, please just be aware of what’s happening when you go down there,” he implored.

“The sea in particular. Stop and watch what the sea is doing. Please be aware of your surroundings - we want to avoid anything like this.”

The woman’s family did not want her name released at this stage.

“Local police have applauded the fantastic help and work of the local Rakaia Hutts residents for all they did in this terrible situation,” said a police spokesperson.

“We would also like to thank other emergency service personnel including the local fire and emergency teams, ambulance staff, and helicopter services that turned up to help in any way possible.”