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Senior Sergeant Glenn Wilkinson, of Queenstown, said police were called at 7.50am to the incident, on Park St, at the bottom of Adelaide St.
The truck had to be lifted by crane from the lake edge.
A St John spokeswoman said one patient was taken to Lakes District Hospital to be treated for minor injuries.
Snr Sgt Wilkinson said the driver initially got out of the truck, but was hurt when he attempted to get back into the cab "to stop it rolling".
He said the truck ran into part of a stone fence and damaged a nearby light pole.
Queenstown Lakes District Council media and channels adviser Sam White said no rubbish or chemicals from the truck entered the lake and a small leak from the vehicle was quickly contained and absorbed on land.
The police commercial safety team was investigating the cause of the crash, as was Waste Management.
Waste Management South Island manager Greg Slaughter said the company’s safety and risk executive flew to Queenstown to lead the investigation.
"We ... apologise to residents for the disruption caused," Mr Slaughter said.