An Alexandra man has become a second time rescuer alongside a childhood friend after leaping into Lake Dunstan to save a man whose ute had taken a icy plunge.

Police publicly praised the quick thinking actions, as the man was taken to Dunstan Hospital in a serious condition.

Alexandra resident Regan Healey, 42, was driving home on State Highway 8 on Thursday when he saw the erratic oncoming ute about 5.15pm.

"He was coming towards me and was wobbling all over the road within his lane," Healey said.

"As he passed me I looked in the rear vision mirror to see him go off the bank."

Healey spun his car around and headed back to help.

Fortunately, the truck had stayed on four wheels, he said.

It was by pure chance that his high school mate Benji Saunders was travelling in the car behind him.

Saunders was already helping the driver out of the water when Healey arrived.

"He [the driver] wasn't getting himself out," Healey said.

The car was about 20 metres into the lake, and submerged up to the bonnet, Healey said.

"He was conscious when he got him to the bank and then he deteriorated very quickly.

"We took care of him until the ambulance arrived."

Healey was well versed in first aid from his work as a lineman, and from the five years he was in the Alexandra Fire Brigade.

Yesterday, Constable Leon Burdett said the public did a wonderful job helping the man escape before emergency services arrived.

"I'd just really like to thank the group who rushed to the man's aid and got him out of the lake, we're really grateful," he said.

The ute had since been removed from Lake Dunstan and an investigation into the cause of the crash was under way.

Healey's quick thinking first made headlines in 2016 for when he saved the life of a choking 9-year-old.

Healey had been in Auckland at the time to attend the New Zealand Tattoo and Art Festival.

He was eating at a restaurant in Burswood when he noticed a mother panicking, the wee boy about to pass out.

Before he knew it he was right in the middle of it.

Healey told the Otago Daily Times at the time the young boy could not breathe.

He had used the Heimlich manoeuvre to clear the boy's throat.

"I got that out - along with everything else he'd been eating."

Today Healey told the Herald he was still in touch with the boy's family.