RedactedNarrative: Vessel 1 containing three occupants was motoring around lake. Operator of vessel 1 stopped to allow one occupant (witness) to get into water and onto tube. Occupant 1 began to struggle and occupant 2 (deceased) went into water to assist occupant 1 and became exhausted and slipped below surface of water. Operator and occupant 1 went back to shore to awaiting personnel.