Police said the teenagers had set out from the Omakau Bridge about 2.15pm for short a trip downstream to another bridge, apparently aboard two kayaks, a lilo and another inflatable.
The trip had been expected to take about 90 minutes, and family members were waiting at the nearby Ophir Bridge, but the youngsters did not rendezvous as expected, travelling further into the gorge.
"They certainly would have been pretty worried," a police spokeswoman said about the family concerns.
Initially good weather conditions in the area, north of Alexandra, were a positive factor — "it was 30degC when we first started looking for them", she said.
Police were notified about 5.55pm, and a police search and rescue operation, backed by LandSAR volunteers, swung into action.
Alexandra helicopter pilot Doug Maxwell flew a two-seater Cabri G2 helicopter above the river in a bid to locate the teenagers, believed to be three boys and a girl.
He managed to quickly locate the missing quartet about a third of the way into the gorge, near the first intake to the Manuherikia irrigation scheme.
He left his flying companion, Alexandra resident Mark Hutton, with them to provide support and help lead them to safety via a nearby track.
About 8pm, the teenagers were taken out of the area with the help of a police four-wheel drive vehicle and others owned by their parents, and driven back to the Chatto Creek Tavern car park search base.
