RedactedNarrative: WHILE GOING THROUGH A RAPID, VESSEL GOT TURNED SIDEWAYS AND SURFED TEMPORARILY.  WATER SWAMPED THE VESSEL, WASHING ALL OVERBOARD.  VICTIM STRUCK HIS HEAD AT SOME POINT WHILE SWIMMING, BUT DIDN'T KNOW WHEN OR ON WHAT.  THIS AREA IS CONSIDERED CLASS IV WHITEWATER AND WAS FLOWING AT APPROXIMATELY 3,800 CFS.