Ardent Leisure admitted breaching the Work Health and Safety Act and exposing individuals to a risk of serious injury or death.

Cindy Low, Kate Goodchild, her brother Luke Dorsett and his partner Roozi Araghi were killed when a water pump on the ride malfunctioned, causing water levels to fall dangerously low.

Two children Ebony Turner, and Kieran Low, then 10 and 12, escaped without physical injury.

The tragedy unfolded as their raft collided three times with another that was stranded on the conveyor belt in low water on October 25, 2016.

Workplace Health and Safety prosecutor Aaron Guilfoyle told Southport court on Monday that the stranded raft was lifted vertically before it dropped to a horizontal position.

The continued movement of the conveyor pulled the doomed raft to into the mechanism.

"It ripped pieces of fibreglass from the raft which shook violently causing Ms Goodchild and Mr Dorsett to fall," Mr Guilfoyle said.

"Ms Turner was held dangling in her seat by the velcro seatbelt and Roozi Araghi and Cindy Low seated at the rear of the raft were pulled into the moving components."

Mr Guilfoyle told the court that while the pump failure was the direct cause of the accident, there were other factors to be considered.

He outlined a litany of failures to adequately ensure the ride was operated safely including poor maintenance and inadequate shutdown procedures.

Previous safety audits revealed a water level safety sensor which could have prevented the accident would have cost less than $3000.

The company also failed to provide information, training, instruction or supervision necessary to protect people from risk.

The pump malfunction was the third that day and the fifth in a week, and no automated shutdown function was installed despite recommendations.

"The ride had been in operation for 30 years the pumps were bound to fail at some point," he said.

"There were failures to implement the control measures which would have minimised or eliminated the risk in the circumstances of a pump failure.

"They are as much the cause as the pump failure."

Kim Dorsett, the mother of Mr Dorsett and Ms Goodchild, was in court for the sentence joined for the first time by Ms Goodchild's daughter Ebony Turner who survived the tragedy.

In a moving statement, Ms Dorsett fought through tears, saying she cried "for my lost children every day".

To this day, she said she was haunted by Ebony's words.

"'I could not find mummy' - these words have become recurring nightmare words that will stay with me until my dying breath.

"I have never been so alone and isolated as I have become in grief."

Ms Dorsett said every day that she wakes she is disappointed.

"I have to have another day in this hell.

"A broken heart has no words."

Ardent's senior counsel Bruce Hodgkinson opened submissions with an apology to the families and all those affected by the 2016 tragedy.

He told the court that safety and staff training at the park had been completely overhauled.

"Ardent and Dreamworld have engaged frequently with the regulator with unwavering cooperation," Mr Hodgkinson told the court.

"It has accepted responsibility for this tragedy and has taken substantive steps to improve safety across the whole of the park."

Magistrate Pam Dowse said the company had failed in its primary safety duty to the public.

She found the company knew of the risk of pump failure and the risk of rafts overturning before the accident.

"Complete and blind trust placed in the defendant by every person who rode the Thunder River Rapids ride and those guests were extremely vulnerable," Ms Dowse said.

Australian Associated Press