MELBOURNE (Reuters) - Australia's Dreamworld theme park will permanently shut a water ride on which four people were killed last month, owner Ardent Leisure Group said on Wednesday.

Two men and two women died in October after getting trapped under an upturned raft on the Thunder River Rapids ride at Dreamworld, near the Gold Coast tourist district in Australia's northeastern state of Queensland.

Ardent Chief Executive said the ride would be decommissioned out of respect for the memories of the victims and their families.

"The closure of the ride is the only respectful and appropriate course of action," Ardent Chief Executive Deborah Thomas said in a statement.

Engineering firm Pitt & Sherry has begun an external review of all Dreamworld and Whitewater World rides and operating systems, separate from an internal review of every ride in the park, which has been closed since the tragedy, Thomas said.

"No ride at Dreamworld will operate until the Workplace Health and Safety Audit has been completed and unless it passes the multi-level internal and external review process," she said.

Ardent shares have slumped 21 percent since the accident.

(Reporting by Sonali Paul; Editing by Ruth Pitchford)