Agree with the likelihood it is a Seabee amphibian aircraft. However, I think it is likely a case of drug runners using the plane to delivery a drug payload to people awaiting in boats on Lake Norman. Then, the aircraft would have been deliberately sunk since it could have been too low on fuel to fly back to where it came from. The risk of notice had it landed to refuel at a nearby airport outweighed the loss of the aircraft.
The reason I say this is because a legitimately owned aircraft would have been recovered or at least reported. Worst case if the pilot died in the crash and lies at the bottom, odds are that a relative would have signaled the alarm. Dirty truth is that a number of these aircraft used in drug transport are stolen and used once, then abandoned or deliberately destroyed. When you can make millions off just one successful delivery, the value of an aircraft worth something in the $50,000 to $250,000 range isn't a big deal, especially as repeated use exposes the drug coyotes to surveillance and capture.
Delivering the payload in the middle of Lake Norman, especially at night, would be a good way of escaping notice, with the added advantage of dumping the drug payload to the bottom of the lake should an unlikely encounter with law enforcement result on the lake. Then, boats laden down could go to any remote shoreline and transport to waiting vehicles. It would be very difficult for law enforcement to anticipate the delivery and even harder to intercept.
Ken
oops. Plane flipped and sank. Pilot got out and just left it there. The Old CAA isn't like the FAA of today.