THE PILOT DEPARTED NAPLES MUNICIPAL AIRPORT, NAPLES, FLORIDA, VFR ON A PERSONAL FLIGHT AT 1130 HOURS. THE AIRPLANE WAS OBSERVED CONDUCTING TOUCH AND GO LANDINGS AT THE MARCO ISLAND MUNICIPAL AIRPORT, MARCO ISLAND, FLORIDA BETWEEN 1300-1400 HOURS AND DEPARTED AT AN UNKNOWN TIME. THE AIRPLANE WRECKAGE WAS INITIALLY SPOTTED AT 1700 HOURS IN UNKNOWN BAY, BUT WAS THOUGHT TO BE A SUNKEN BOAT. THE CIVIL AIR PATROL SPOTTED THE AIRPLANE AT 1925 HOURS AND NOTIFIED THE AUTHORITIES, WHO RESPONDED TO THE CRASH SITE. AIRCRAFT RECORDS AND HOBBS METER IN THE AIRPLANE, INDICATE IT HAD BEEN OPERATED 4 HRS & 36 MIN. AIRCRAFT PERFORMANCE CHARTS INDICATE FUEL EXHAUSTION AT 4 HRS & 24 MIN. THERE WAS NO EVIDENCE OF FUEL AT CRASH SITE OR PURCHASE OF FUEL BY THE PILOT. PHYSICAL EVIDENCE INDICATES INFLIGHT LOSS OF CONTROL. THE AIRPLANE STALLED AND SPUN TO THE LEFT AND IMPACTED THE WATER. THERE WAS NO EVIDENCE OF ANY POWERPLANT, AIRFRAME OR FLIGHT CONTROL FAILURE.