Their four-wheel drive vehicle had overturned in the swollen river, which feeds into Lake Ohau.
Severe weather warnings were in place for the headwaters of Otago's main lakes and rivers until late yesterday, with up to 90mm of rain expected about the main divide and 60mm within 15km east of the divide.
On Saturday morning, two men and two boys spent more than two hours sitting on their upturned 4WD in raging waters before being plucked to safety, cold and wet but uninjured.
The four activated a distress beacon about 9am. This was credited with having saved their lives.
He said heavy rain was still falling when rescuers arrived at 11.10am. The team used ropes to reach the stranded group and the helicopter then hovered to pick up each person. It took about 45 minutes to rescue them all.
"The floodwaters were rising and forecast to increase ... the channels were deep and fast-flowing," he said when contacted yesterday.
"Luck was on their side."
The weather around Aoraki Mt Cook yesterday had changed little and the rain had not let up, he said about 3pm.
Over the weekend until 8 o'clock last night, Environment Canterbury Mt Cook rain station recorded 157mm.
Senior Search and Rescue Officer Tracy Brickles said the "rescue reinforces what we already know: distress beacons save lives".
"They're not just for trampers, hunters or boaties - distress beacons can be lifesavers for anyone who's heading into a remote location," she said.
"Undoubtedly, the rescuers saved four lives," she said, giving thanks to the Helicopter Line for getting Aoraki Mt Cook Department of Conservation Search and Rescue Team members to the scene, while the Rescue Co-ordination Centre NZ sent in the Otago Regional Rescue Helicopter to assist.
The four were flown to a nearby hut, then picked up by the Otago Regional Rescue Helicopter and taken to Mosgiel, from where they were able to go home.
For the Southern Lakes area MetService was forecasting "possibly heavy" rain today, with snow to 900m at first, easing to isolated showers and clearing by afternoon.
"Before dawn, [today] there is a moderate risk of thunderstorms about Fiordland, Stewart Island and the south coast of Southland.
"These thunderstorms may bring localised heavy rain with intensities of 10mm to 20mm per hour and hail," MetService said.
The Routeburn Classic run at the weekend was cancelled because of the poor weather.
