Dreamworld staff feared for the safety of the Thunder River Rapids ride which killed four people 15 years before it malfunctioned.
A coronial inquest heard a worker at the theme park sent an email saying: "I shudder when I think if there had been guests on the ride" after an incident in 2001.
New Zealander Cindy Low, Kate Goodchild, her brother Luke Dorsett and his partner Roozi Araghi lost their lives in the tragedy on the Gold Coast, Queensland in October 2016.
On the opening day of an inquest into the tragedy, counsel assisting Ken Fleming QC revealed several earlier incidents had occurred on the Thunder River Rapids ride.
Fleming said one incident, in January 2001, had resulted in several empty rafts colliding at the unloading point of the ride.
Lead police investigator Detective Sergeant Nicola Brown said the water pump on the ride had stopped working twice in the hours leading up to the fatal incident.
Brown told the inquest the pump failed at 11.50am and then again at 1.09pm before being reset by engineers.
The inquest heard the incident was disturbingly similar to the one which resulted in the deaths of the four people in 2016.
When the raft containing victims as well as two children collided with another raft, it flipped over and dropped the guests into the conveyor system.
All four victims were killed instantly from compressive and crushing injuries.
Goodchild's 12-year-old daughter and Ms Low's 10-year-old son were on the raft which flipped at the end of the ride, but survived.
The inquest heard the emergency stop button on the ride could have shut it down "in two seconds", the Courier Mail reported.
Brown said the button was "totally unmarked" and a ride operator was told "not to worry about that button, no one uses it".
The families have sought answers and relatives of New Zealand-born Low have said how they hoped the probe would prevent others from suffering "such enormous heartbreak".
Dreamworld announced it would demolish the Thunder River Rapids Ride in November 2016.
• October 25 - The Thunder River Rapids Ride malfunctions and causes the deaths of Cindy Low, Kate Goodchild, Luke Dorsett and Roozi Araghi.
• October 26 - Dreamworld announce plans to reopen on October 28. The reopening is later cancelled following advice from police to scrap the plans.
• October 27 - Parent company Ardent Leisure hold its AGM in Sydney. Then CEO Deborah Thomas comes under fire for not speaking directly to the victims' families.
• November 3 - New Zealand ex-pat Cindy Low's funeral is held on the NSW Central Coast.
• November 5 - Roozi Araghi's funeral is held in Sydney.
• November 7 - Kate Goodchild and Luke Dorsett are farewelled at a funeral in Canberra.
• November 9 - Dreamworld announces it will demolish the Thunder River Rapids Ride.
• November 25 - Workplace Health and Safety auditors issue seven improvement notices and three prohibition notices following inspection of Dreamworld and WhiteWater World.
• December 10 - WhiteWater World fully reopens and Dreamworld partially reopens, with many of the big rides undergoing safety reviews.
• January 6 - Ardent Leisure announces revenues have plummeted by 63 per cent across Dreamworld and WhiteWater World.
• April 26 - Deborah Thomas announces she is standing down as Ardent Leisure CEO. She later leaves the business with a $731,000 payout.
• June 30 - Ardent Leisure report $62.6 million loss for the financial year. Crowds at Dreamworld estimated to have dropped by as much as 30 per cent.
• September 28 - A Workplace Health and Safety investigation is completed. Industrial Relations Minister Grace Grace says charges against Dreamworld are possible.
• October 13 - Police conclude its report into the incident and deliver a two-volume brief to the coroner.
• June 18 - Coronial inquest hears there was a previous similar incident on the Thunder River Rapids Ride in 2016