The twin brother of a teen who died in a flash flood at a West Auckland swimming hole has joined schoolmates to raise money for the rescue helicopter which saved his life.

On February 3, siblings Denver and Mitch Woolley and their mates Nathan Phillips, Jason Lee and Sosiveta "Sosi" Turagaiviu were swimming at Cascade Falls in the Waitākere Ranges.

They had earlier been paintball shooting, where the last photo of them all together was taken.

A sudden downpour caused a flash flood in the normally placid creek below the swimming hole, creating a torrent of debris-filled water.

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Nathan and Jason were able to swim to the riverbank but the other boys were swept away.

Jason Lee (left), Mitch Woolley, Sosi Turagaiviu, Denver Woolley and Nathan Phillips, pictured at a paintball park hours before the tragedy. Photo / Supplied
Jason Lee (left), Mitch Woolley, Sosi Turagaiviu, Denver Woolley and Nathan Phillips, pictured at a paintball park hours before the tragedy. Photo / Supplied

Denver managed to hold on to a tree and was eventually winched to safety by the Auckland Westpac Rescue Helicopter.

Tragically, Mitch and Sosi were killed.

The boys all attended Massey High School (MHS), although Mitch had left to pursue an engineering apprenticeship.

On Friday, a fundraising gala was held at the school to raise money for the rescue helicopter service.

Denver and his family have previously met the crew who saved him, but he was keen to do more to show his appreciation.

"They saved my life," the teen survivor said.

The school community raised $10,000 through the gala and Denver thanked his friends for their support, as well as the team at the Westpac Rescue Helicopter.

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Members of the crew who rescued Denver were at the gala, including intensive care paramedic Russell Clark.

On the day of the rescue, pilot Rob Arrowsmith hovered in driving rain and gusty winds at a height of 60m, as Clark was winched down under the watchful eye of crewman Ati Wynyard to save Denver.

Clark spoke of the incredible moment they finally spotted the terrified boy.

Denver Woolley is winched to safety by Auckland Westpac Rescue Helicopter intensive care paramedic Russell Clark on February 3. Denver was caught in flash flooding in West Auckland. Photo / Supplied
Denver Woolley is winched to safety by Auckland Westpac Rescue Helicopter intensive care paramedic Russell Clark on February 3. Denver was caught in flash flooding in West Auckland. Photo / Supplied

"We never gave up hope," Clark said.

Based on the limited fuel left at that stage they knew they had to get to him immediately, he said.

"He had fast-flowing water on either side of him."

They estimated it was moving at 30-40km/h.

"[We thought] we've got one shot at this and we've got to get him out."

It was rare that they performed a rescue in such swiftly moving water, he said.

"It's not something we do every day.

"We could have easily been washed away."

MHS head prefect Janneke Grundemann said the fundraiser was really important to students and staff at the school.

"We've seen the impact this had on Denver and his family," she said.

The loss of Mitch and Sosi was felt deeply among the students.

"It was very hard, especially because it was at the start of the year and coming into the year on such a heavy, sad note - it was not easy for anyone."

The entire school wanted to back the cause and "give them the recognition they deserve".

Fellow prefect Emma Jamieson said it was great to give back to such a good cause as they ended the year.

"It was an awesome event to bring the community together and get everyone talking about it."

MHS geography and tourism teacher Sadie van der Kraaij also played a big role in organising the gala.

Flash flood survivor Denver Woolley with his rescuer intensive care paramedic Russell Clark of the Auckland Westpac Rescue Helicopter. Photo / Doug Sherring
Flash flood survivor Denver Woolley with his rescuer intensive care paramedic Russell Clark of the Auckland Westpac Rescue Helicopter. Photo / Doug Sherring

The appeal meant a huge amount to the students, she said.

"There were certainly students who volunteered that don't normally put themselves forward and they did that for Denver."

Auckland Rescue Helicopter Trust communications manager Lincoln Davies said the team were "absolutely delighted" with the fundraiser.

"Their efforts will help fund two rescue helicopter missions - potentially two missions where lives will be saved," he explained.

"With the families' blessings we are dedicating two missions in memory of Sosi and Mitch, and with our sincere gratitude to Massey High School for their amazing generosity."