The duo rushed into the benign swell with their rescue tubes in tow.
They rapidly reached the swimmers where the teen, Swannix said, had begun to lose consciousness.
A nearby surfer had noticed the rescue unfolding and paddled over to help.
Swannix said the guards clipped the teen into a rescue tube and used the surfer’s board to keep her further afloat.
The pair then swam the group back to shore - only three of whom needed to be rescued.
In the minutes it took to hit land, the teen had become unconscious and was not breathing.
Swannix said the guards immediately started CPR.
Shortly after, the patient started breathing again.
Guards then provided first aid until the Northland Rescue chopper arrived.
Other emergency services - a St John Hāto Hone ambulance and the Whangārei Heads Volunteer Fire Brigade - assisted.
More than 100 people had flocked to the coastal hotspot to make the most of what Swannix described as “glorious weather”.
But around 1.30pm, the tide was at its lowest and the beach its most dangerous that day.
“At low tide, rips were opening up all along the beach,” Swannix said.
Flash rips were especially risky as they can occur without warning and subside rapidly. Surf Lifesaving New Zealand warns that the temporary rips can easily pull swimmers out to sea quickly from areas that were safe just moments earlier.
Swannix said the guards had moved the flagged area quite a bit already that day to manage the risks of flash rips.
“Those swimmers were doing the right thing - they were making sure they stayed between the flags, they were listening to the lifeguards - sometimes these things just happen.
“But it’s what we’re there for. It’s our job and we identified that they needed help and we brought them to shore,” Swannix said.
Around 45 minutes before the family was saved, Whangārei Heads surf lifeguards had pulled three children to safety from a flash rip using tubes.
Swannix said Ocean Beach had been “pretty dangerous” this summer.
Lifeguards had completed a high volume of rescues but members of the public had been heeding their safety advice, he said.
“People need to make sure they stay within their abilities and listen to lifeguards. If you do get into trouble, put your hand up, relax and float on your back.”
Swannix praised the “amazing” lifesaving work carried out by the guards over the weekend.
“You always look back after incidents like this and think about what could have gone better but in the end we saved someone’s life and that’s amazing, that’s what we’re here for.”