Recently, four people were killed at Thunder River Rapids in Dreamworld, a theme park in Queensland, Australia. It is still uncertain how two people were thrown from the ride and two others were pinned underneath as Australian authorities continue to investigate.
As a result of this incident, Walt Disney World and other theme parks have closed their similar river rides pending the result of the investigation in Australia. No incidents of a similar nature have occurred at Disney, however, authorities want to be sure if an unknown hazard is present in Florida and California they want to correct it before a similar tragedy happens again.
Disney World, Islands of Adventure in Universal Studios, and the Six Flags parks all have rides relatively identical to the Australian version. I will post more information as it becomes available.
Tourist safety is of utmost importance to all the parks and they all want to err on the side of caution for the time being.