Mr Black said the Christchurch man and his two friends, each in separate boats, were not supposed to be in the section of the Kawarau River.
The men were travelling in jet-boats along the river from Frankton at 2pm, when they reached a rapid. The first two men managed to steer through but the third man "got his nose caught in a rapid where he shouldn't have", Constable Terry Wood said.
After the boat filled with water, its engine stalled and the driver jumped from the boat into waist-deep water.
Police were alerted by a passing cyclist, Const Wood said.
Police had three options - winch him out by helicopter; call in a commercial jet-boat; or go down through the bush on foot.
The third option was thought the safest as the rapids were "too big" and it was too windy for a helicopter rescue, so Const Wood and a medic "bush bashed" their way down to the man.
The rescue helicopter hovered above.
The man could possibly have climbed up but at that point he "would not have known what was above him ... There was a vertical face above him", Const Wood said.
The man was not injured in the incident. His water-laden boat was lifted out by a helicopter and placed on nearby land.
