Port Otago Takutai dredge operators Leon Snoeck and John Laughton responded to a call for help from emergency services on their radio on Tuesday afternoon.
They arrived to find the man, in his 70s, clinging to the side of his boat in Sawyers Bay.
"He was unconscious and pretty rigid," Mr Laughton said.
"His arms were stuck up in the air, probably from holding on to the boat.
"He was still breathing, but he was severely hypothermic — he was quite blue."
"He’s clearly a survivor to hang on for that long — very, very lucky to be alive to be in cold water that long without a lifejacket.
"He’s a fighter."
The duo said most other people would probably have died.
The man is believed to have been in the water for about two hours after falling from his kayak following a visit to his boat, which was anchored in the bay.
Mr Snoeck said the rescue helicopter was already at the scene when they arrived, but its crew was having difficulty winching the man out of the water.
So the helicopter moved away and the duo were asked to help pull the man out of the water.
"We managed to get him on to the bow of the vessel and brought him ashore.
"He was quite heavy. John and I are both reasonably strong and it was a big struggle.
"He was a stocky man, definitely."
Once ashore, St John staff put the man into the rescue helicopter because the bank up to the road in Roseneath was too steep to carry him up to the ambulance.
He was flown straight to Dunedin Hospital in a serious condition.
Mr Snoeck said they were dredging in the harbour near the Harbour Basin when the call came through.
They shut down the equipment and deployed their tender — a small aluminium boat, which is usually used to ferry crew and equipment to the dredging barge.
"We heard there was a 70-year-old man in the water.
"I thought, ‘We need to get down there as quick as we can’ — no-one else was responding so I thought, ‘We could only try’."
He said the tender was an unlikely rescue boat but "it did the trick".
Their work colleagues gave them plenty of "pats on the back" for their efforts.
"It’s nice to be able to help when we are needed," Mr Snoeck said.
"I’d hate to be in that situation and not have someone help me."
Following the rescue, the duo returned to the man’s boat to get his cellphone and keys, and put his kayak on board.
Unfortunately, it appears there was no rest for the good Samaritans after the rescue.
"We had to go back to work. We’d left the vessel [Takutai] unattended.
"So we went back and carried on digging."
The man remains in Dunedin Hospital, but for privacy reasons, the hospital declined to provide a patient condition update.
