Eighteen year-old Kieran Whyte pulled his step-brother Todd Pinnegar, 19 of Mount Pleasant, and girlfriend Samantha McPhersen, 16 of Goolwa, to safety when they drifted several kilometres off shore.

The Victor Harbor teenager and his friends were "just playing in the waves" for an hour outside a Beach Road cafe before realising they had been swept into trouble.

"Suddenly we noticed how far we had been dragged out to sea and how big the waves had become," Kieran said.

"My (step) brother freaked out and couldn't move, so I swam with him for about two kilometres until he could stand up."

The danger far from over, Kieran headed back into the rip for a second resuce when he realised his girlfriend was still in trouble.

"Waves were crashing over my head and I couldn't breathe," Goolwa teenager Samantha McPhersen said.

Kieran said all he could think about was getting Todd and Samantha out of the water.

"I thought I was gone," he said.

"I was exhausted...but I just wanted to get them to safety and I wouldn't stop until I did."

Kieran's sister Alana Whyte assisted Todd on the beach and kept him conscious while her brother performed the second rescue.

Watching from the beach, Celine De Perlinghi ran into the water to save a third teenager.

Todd was taken by ambulance to the Royal Adelaide Hospital with suspected spinal injuries, but was later found to be suffering from hypothermia. Kieran and his friends hope the incident will make people aware of the potential dangers of swimming at Goolwa Beach.