RedactedNarrative: According to the operator, V1 was stopped near the "no boats" buoy in the vicinity of the swimming area at Dam Site Park.  V1 was not anchored and the motor was not running.  He stated there was a significant chop on the water due to all the boat traffic, causing V1 to sway back and forth.  The victim was attempting to do a back flip off the port side passenger seating area; but he jumped while V1 was swaying and went more vertical than horizontal and did not clear V1.  Victim hit the back of his head resulting in a 12 cm laceration across the top/back of his head requiring multiple staples.  
   
  No alcohol was on board or had been consumed by anyone.