Three family members were hurt, one of them critically, when a log ride at the Castle Park amusement park in Riverside malfunctioned on Saturday afternoon.
The accident took place about 4:30 p.m. at the park at 3500 Polk Street in Riverside.
One patient, described by witnesses as a woman, was taken to a hospital in critical condition, Riverside City Fire Department Battalion Chief Bruce Vanderhorst said.
Two adults and a child were thrown from a log-shaped car once it reached the bottom of a waterslide, according to Vanderhorst. One of the adults was hospitalized in critical condition.
The other two patients, including a 10-year-old boy, were being treated for minor injuries, fire Capt. Brian Guzzetta said.
Officials previously reported a total of five people were injured in the accident.
It initially appeared a water pump used to slow the log ride down malfunctioned, causing it to toss the passengers out, he said.
Guests told KTLA the ride had been closed earlier in the day, but reopened around 2 p.m.
Castle Park spokeswoman Michele Wishmeyer said an investigation was underway.
"We've been a part of this community for decades and we take safety very seriously," she said. "There will be a full investigation on our part, and the Department of Safety and Health is on their way here to conduct their own investigation as well."
KTLA's Judy Oehling contributed to this report.