Among those hurt was a 16-year-old Australian girl who suffered facial injuries and needed emergency treatment for misaligned teeth and a man who suffered a broken arm.
Go Orange is a former brand of South Island tourism company Wayfare, which rebranded as RealNZ in October.
Its operations include the International Antarctic Centre, Cardrona Alpine Resort, Treble Cone and Real Journeys.
A Maritime New Zealand prosecution of Go Orange Ltd and the driver, Levi Kjeld Prier, resulted in both admitting a single charge of breaching the Health and Safety at Work Act.
After a sentencing hearing in the Queenstown District Court in December, Judge John Brandts-Giesen reserved his decision.
His written decision, issued on February 23, was released to the Otago Daily Times yesterday.
Judge Brandts-Giesen said Prier, who drove for the company on a casual basis, was found to have elevated levels of party drug MDMA (ecstasy) and the hallucinogen MDA in his system.
His breath-alcohol level was 640mcg.
The combination of drugs and alcohol could mean users "feel like they are driving better when their actual performance may be severely impaired", he said.
A Maritime NZ investigation found Prier misjudged a sweeping right turn while travelling at about 80km/h, causing the boat to strike a rock outcrop extending from the riverbank.
The boat then hit a second rock face at about 40km/h.
He claimed to have "forgotten" he had to work the following day but nevertheless turned up knowing he was still influenced by drugs and alcohol, Judge Brandts-Giesen said.
That exposed the passengers to the risk of serious injury or death, the judge said.
"He should have reported to his employers that he could be impaired, and been assessed before going out on the boat."
The investigation also found the company had decided in 2019 to exclude casual drivers from the list it provided to a third-party testing company.
The intention was for full-time staff to be tested more frequently.
That "error of that logic" had been recognised and the testing system changed.
In setting fine amounts, the financial positions of both defendants had been heavily affected by the impact of Covid-19, Judge Brandts-Giesen said.
As a result, he reduced the company's fine from $225,000 to $150,000 and, for Prier, from $30,000 to $10,000.
He ordered reparation costs to be split equally between the defendants: $1593 to the injured girl for her emergency dental treatment, and $15,000 for ongoing treatment required and emotional harm. Her father receives reparation of $6500 for emotional harm, and every passenger who filed victim impact statements receives $2500 reparation for emotional harm.
The defendants' contribution to the cost of prosecution has yet to be determined.
