Footage has emerged of 2m sea swells at the Rakaia River mouth just hours before a woman died in the water after getting stuck on a quad bike. 

The woman died after being swept into the water on Saturday. 

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

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. 

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. 

Local fisherman Nico Van der Zwet shared a video of the area in a bid to highlight how treacherous conditions could become. 

The video shows a number of people fishing near where the woman died. And it shows the surf building. 

“I was at the river mouth earlier that day and took some video of the time I spent there. Before heading down I checked the marine forecast and it was predicted the swell would rise to 2 metres later in the day,” Van der Zwet told the Herald. 

“I headed down just before 10am and on arrival talked to a couple of the local fishermen. As I was fishing, about half an hour after arriving I noticed the sea was beginning to rise so I started video recording.” 

He said several other men were fishing nearby in the “gut” - the narrow before the river enters the sea. 

“A little later they were forced to to move as the sea started washing over. I spoke to one of them on his return warning him that it’s not worth the risk,” he explained. 

“As I continued fishing the sea got worse and knowing that it was still two hours before high tide, I decided to head away. 

“I could see that some of the larger swells were beginning to wash over in a lower section of the beach I had to cross in the distance. 

“As I arrived at that low section of beach, which is about 200m long, the swells were not that big and I managed to cross it safely, but there was water there.” 

The surf building on the day. Image / YouTube 

Van der Zwet uploaded his footage to YouTube so people " get more understanding of the area". 

“I am very sorry to all those affected in this tragic incident,' he said. 

“Maybe I could have gone back and warned the other fishermen there to leave or stay until the tide dropped?” 

Yesterday Ashburton councillor Russell Ellis told the Herald he had also been to the river mouth earlier in the day. 

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

“It’s a really unfortunate set of circumstances ... Saturday happened to be particularly high seas coming through the low area. 

“It caught these people and some others out. 

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

Anna Leask is a Christchurch-based reporter who covers national crime and justice. She joined the Herald in 2008 and has worked as a journalist for 18 years with a particular focus on family and gender-based violence, child abuse, sexual violence, homicides, mental health and youth crime. She writes, hosts and produces the award-winning podcast A Moment In Crime, released monthly on nzherald.co.nz