McDowell Mechanical owner-operator Ken McDowell was "gobsmacked".
"I can't figure out why someone has done this," Mr McDowell said.
The diesel engineering workshop used the forklift for heavy lifting, and it was a setback for the company to have the $6000 machine written off, he said.
Following the direction of the voice, he discovered a broken chain-link fence, and a wrecked forklift lying semi-submerged in the stream below.
When Mr Mortimer discovered the forklift, he rang emergency services and waved down passing motorists Jim Edmond and Nigel Windle, who were on their way to a plastering job.
Both men slid an estimated 7m down the steep bank, finding a young man pinned on his back while supporting himself with one hand in the waist-deep water.
"He said he had been in the water for 25 minutes, and I reckon in another 10 minutes he could have passed out and slipped under the water."
Mr Edmond worked to free him from a submerged forklift strut while getting directions from Mr Windle.
"It was pretty damn cold down there."
Emergency services arrived just as the man was freed, and he was treated by St John staff.
Senior Sergeant Steve Aitken said the man, who appeared to be intoxicated, was believed to have climbed a fence at a property off Kaikorai Valley Rd, before allegedly taking the forklift.
The 19-year-old drove the forklift 20m before crashing through a chain-link fence and plunging into the stream.
He was taken to Dunedin Hospital for observation.
"He was lucky he was not killed," Snr Sgt Aitken said.
The unemployed man had been charged with burglary, unlawfully taking a vehicle, driving while disqualified and breaching bail. More charges were likely, Snr Sgt Aitken said.
He was remanded in custody and will appear in the Dunedin District Court on December 21.
