Area Prevention Manager Senior Sergeant John Fookes said the three young men were rescued from the Kawarau River near Queenstown when their swimming plans went awry.
He said the trio entered the river upstream of Rafters Rd in Gibbston about 3.15pm and immediately got into difficulty.
One managed to get himself safely on to rocks but the other two were swept further down the river.
He said one managed to get to a bank on the opposite side of the river, while the second was pulled out by a passerby who jumped down a bank to help.
Owing to the treacherous nature of the river, a rescue helicopter was called in and within half an hour the crew had helped all involved to safety.
"This was an incredibly close call for the young men, and it was so lucky someone saw what was happening and heard the screams for help.
"A very short distance downstream the river hits the Nevis Rapids, which become grade 5 and are incredibly unforgiving."
He said that had the trio been swept any further downstream, "we would have been dealing with an entirely different scenario".
He said anyone swimming in rivers, or exploring the outdoors should do their research and treat the environment with respect.
