The owners of Queensland theme park Dreamworld have paid out millions in compensation, but are expected to pay several times more.

Ardent Leisure has paid out more than $5 million in compensation claims to family members of the victims killed in the 2016 Thunder River Rapids tragedy, as well as emergency responders and witnesses.

The tragedy caused the deaths of four people on October 25, 2016.

Several people were flung into a mechanised conveyor when a water pump failed, causing the raft they were riding to collide with another and partially flipped.

Park managers gave evidence before a 31-day coronial inquest in 2018, revealing that staff did not have adequate training, incidents went unreported, and some rides were not properly maintained.

The company has now settled over 20 compensation lawsuits, but more are still ongoing.

Reports this week suggest there are some compensation cases that have not started yet, as they will rely on the findings of the coronial investigation, which started three years ago.

Legal experts have told reporters that the true cost of the tragedy could be as high as $20 million.