Dreamworld's failure to install a safety feature that would have cost no more than $3000 was the "primary" cause of the 2016 Thunder River Rapids ride tragedy.
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A safety audit undertaken following the deaths of four guests at the Gold Coast theme park concluded if a water level sensor had been installed during a safety upgrade earlier in the year, the tragedy would have been prevented.
Cindy Low, Kate Goodchild, her brother Luke Dorsett and his partner Roozi Araghi died when a water pump suffered an "earth fault" for the third time in a day on October 25, 2016, causing water levels in the ride to drop dramatically.
That left an empty raft stranded on the ride's conveyor before the raft carrying the four victims collided with it and flipped on its side.
An inquest at the Southport Coroners Court into the deaths was shown the report by Safety Related Control Systems on Monday.
It determined installing a water level sensor during an upgrade in February and March 2016 would have added only $2000 to $3000 to the total cost of the works.
"The primary cause of the tragic incident was the lack of a suitable safety-rated water level detection system intergrated to the upgraded conveyor system," the report found.
"Such a safety system could easily have been provided and at a minimal cost."
Contractors who undertook the upgrade said they were never asked to install a sensor.
The inquest heard Dreamworld was considering installing a sensor in a future second stage of the safety upgrade.
It was also revealed the drive motor for the water pumps on the ride, which had been installed in 2006, had a recommended operational life of 10 years.
An electrician who performed regular maintenance on the ride for Dreamworld said he had been scheduled to inspect the water pump two days after the tragedy occurred.
In an email to Applied Electro, Dreamworld electrical supervisor Scott Ritchie made a request for a technician to attend the park due to ongoing faults.
Applied Electro electrician Michael Takac told the inquiry any electrical system faulting as much as the pumps on the Thunder River Rapids ride had been was "concerning".
"It could be multiple things, an earth fault is pretty hard to find ... my advice would be to stop the machine. Investigate it further and identify the fault," he said.
The manufacturers of the pump's drive tested the equipment shortly after the tragedy but were unable to determine what had caused the fault.
Wayne Cox, who was supervising Dreamworld's engineers on the day of the tragedy, said he had been informed of only one of two prior malfunctions on the ride that day.
Mr Cox was unaware his staff had merely reset the pump on both occasions without requesting an electrical specialist attend the site.
The inquest was shown documents revealing there had been nine problems with rafts logged in the weeks leading up to the tragedy, seven of which concerned the two rafts involved in the fatal incident.
Mr Cox said if he had been aware of those issues he would have removed the rafts to determine what problems they may have.
The inquest continues on Tuesday.
Australian Associated Press
