A medical summary read by the coroner said Ms Burnett was found to have a collapsed lung, extensive chest wall injuries and fractured ribs, which affected her breathing ability, as well as a spinal fracture and shoulder injury.
She died of secondary brain injuries.
The competing St John volunteer, Gary Story, of Oamaru, said he recovered Ms Burnett from the water within seconds of the crash and gave her basic assistance on the way into shore. He called the Milton ambulance.
He and others at the inquest said Ms Burnett was initially conscious, walking and talking, but in obvious pain.
She was put in a neck brace and lifted into the ambulance on a stretcher, while a Dunedin ambulance with an "advance" crew was dispatched.
The ambulances met on State Highway 1 between Milton and Dunedin, where an intensive care paramedic was able to assess Ms Burnett, whose condition had deteriorated.
Intensive care paramedic Patrick Bain, of Dunedin, said he noticed she had a compromised airway, but he could not put a tube through her mouth and into her lungs because she had trismus (lockjaw) as a result of losing consciousness while in the Milton ambulance.
Her breathing was assisted on route to Dunedin Hospital with Nasal tubes and a bag mask.
Mr Bain and St John's South Island medical adviser, Dr David Richards, said that if an advanced paramedic was at Lake Waihola with an ambulance Ms Burnett's breathing could have been assisted earlier, when she was conscious and did not have lockjaw, which could have alleviated the extent of brain damage.
Dr Richards said that once she had lockjaw only a paramedic specially trained to administer muscle-relaxing drugs could "intubate" her, and St John had no such paramedics in the South Island.
St John reviewed Ms Burnett's post-crash care and found it was not best practice.
Her airway problem could have been recognised and tended to sooner, and ideally there would be pre-hospital personnel trained in rapid sequence intubation employed by St John Ambulance in the South Island.
Dr Richards said if advanced paramedics and appropriate rescue equipment was available at the race, the outcome of Ms Burnett's death might have been different.
The Milton Boat Club and New Zealand Boat Marathon Commission organised the annual Lake Waihola race and were endeavouring to have advanced St John attendance at future events.
Commission president, club member and race convener Ian Spencer, of Outram, said Ms Burnett's death prompted rule changes.
Ms Burnett was the first person to die as a result of competing in a powerboat marathon race, Maritime New Zealand confirmed at the inquest.
She wore a helmet and life jacket, as required. It was her first experience as a powerboat crew member.
Her brother David Burnett was surprised an ambulance was not at the high-speed powerboat race, as was required at other motorsport events.
"You can pay to have an ambulance on site - you can't use the excuse of being in a rural volunteer area. There should have been an ambulance on site," he said.
Those at the inquest heard Mr Sexton was a suitably skilled and trained powerboat operator, Pure Insanity was in good condition, the race and weather conditions were perfect, pre-race scrutineering was thorough and Lake Waihola more than deep enough.
There was no conclusive cause of the crash.
Mr Sexton thought his boat may have suffered internal damage when it struck a rock at Roxburgh six months prior, but it was scrupulously checked and found to be fine.
Maritime New Zealand maritime investigator Bruce McLaren said it was possible the boat struck the bottom of Lake Waihola, or an object, although there was no physical evidence of it.
Mr Crerar will release his formal findings in due course.
