RedactedNarrative: Vessel left with one passenger onboard at approximately 1500 hours.  Between 1600-1900 hours the passenger decided to go for a swim.  After a short period the passenger began to have trouble.  The operator attempted to use a throw able flotation device but was unable to reach her.  He then anchored the vessel from the stern and went in after her.  The operator was not seen again.  The passenger was picked up by a passing boater a prolonged time later (1-3 hours) still clinging to a flotation device.