Holy Bejeebus!
I hope that the young lady is able to resume a full and active life. Sometimes, the emotional scars are more crippling than the physical. I can only imagine the horrendous guilt that her father must be feeling right now, and hope that he is able to recover as well.
You would think that 5 markers are hard to miss. Maybe he was making a turn fairly close to shore, cut in too close to the shoreline and didn't see the markers as he came around the turn? Hard to say without actually seeing the area. Was he trying to drive and keep an eye on the tuber as well? Perhaps. I thought about the possibility of being blinded by the sun, but the accident occurred mid-afternoon, so a low-lying sun is out.
Here's to hoping for a speedy recovery for all involved.