Water rides are my favorite. I take my youngest one on them whenever I can. She is almost 11. That said, I sit right next to her to monitor her. That is what sounds like was missing here. There wasn't enough supervision. I think water rides tend to be the safest rides… but it always requires supervision.
Most of the time you hear about accidents on a amusement park ride it is usually the fault of the passenger trying to do something they should not while on said ride. All too often the amusement parks will settle out of court rather than spend more money in court fighting the families of these people who like to injure themselves.
Yes, it's an indication of our litigious society. But this was an eleven year old. We have to assume an eleven year old is going to make some poor decisions, and in situations like this they could be dangerously poor. There should have been an adult right there to stop it or they shouldn't have been there st that age.