Two persons were onboard vessel at time of accident.  Passenger states vessel was inbound buncess pass and came to a stop at marker 3 to check the engine because water was not circulating out of the motor.  Deployed anchor.  Operator put vessel in neutral and walked to the stern of vessel and stood on deck near the engine.  Passenger states the operator fell into the water after losing balance.  Passenger threw a line to subject but was not able to take hold.  Subject in water directed passenger to retrieve anchor.  As subject was initially retrieving anchor, she noticed subject in water drifting away towards the opening of the pass into the open water of the gulf.  Once passenger finished retrieving anchor to start the motor and pick up subject she was not able to locate him.  Rescue efforts were not able to locate the subject.  Remains missing
ST. PETERSBURG