RedactedNarrative: Operator 1 was operating vessel 1 on lake wappapello and occupied by six passengers. Operator 1 had the throttle position in neutral and the vessel drifting. Vessel 1 had a tube attached to it and the passengers planned on tubing behind. Passenger 2 left vessel 1 voluntarily so he could tube behind vessel 1. Passenger 2 attempted to board the tube, he was unable to pull himself up onto the tube. Passenger 2 may have suffered a medical condition and became exhausted. Operator 1 did not cause any contributing factors to the death of passenger 2. Passenger 2 left the vessel without wearing a pfd in choppy waves, his swimming ability was weak, he took on water and became exhausted.