RedactedNarrative: Vessel #1 was operating at idle speed southbound on Salt Fork Lake from the boaters beach area. Occupants #3 & #4 were hanging onto the swim platform, with lower bodies in the water, while underway.  Near the area where vessel #1 began to turn westward occupant #3 questioned where occupant #4 was located. Occupant #1 & 2 realized # 4 was missing and began to search and call for him,  he was not wearing a lifejacket. Occupant #3 was recovered nearby the following morning after a short sonar search. The cause of death was ruled carbon monoxide poisoning.      According to the investigator there were 14 empty beer cans on the vessel and both parents admitted to consuming alcohol through the day.