Nothing...what could, or should, they do about it?
This actually happened (but it wasn't a water ride) to DH once in Ocean City, Md. on the Haunted House ride/attraction at the Boardwalk. The car he was riding in jerked really hard around a turn & he actually hurt his ribs/side so badly that he had a hard time walking for several days. This was years ago. I can't recall if he went to the doctor or not, but I think he did. And no, we did not report it to any employees there.