What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
Aircraft departed King Ranch Airport at 1550 with instructor in rear seat and student in front seat. After climbing to 5500 ft the engine began running rough. After leaning, the engine smoothed. After approximately 20 minutes, aircraft descended to inspect a gravel bar on the matanuska river. Engine began running rough again and started to lose power. Carb heat was applied but engine continued to lose power. Attempts to further lean the engine did not restore power and the instructor decided to land on a nearby sand bar. Aircraft came to the end of the sand bar and the main tires rolled into approximately 10 inches of water which caused the aircraft to nose over coming to rest on its back in the river resulting in a cracked wind screen and a small dent to the top of the rudder. No injuries to occupants.
As the FAA filed it
AIRCRAFT DEPARTED KING RANCH AIRPORT AT 1550 WITH INSTRUCTOR IN REAR SEAT AND STUDENT IN FRONT SEAT. AFTER CLIMBING TO 5500 FT THE ENGINE BEGAN RUNNING ROUGH. AFTER LEANING, THE ENGINE SMOOTHED. AFTER APPROXIMATELY 20 MINUTES, AIRCRAFT DESCENDED TO INSPECT A GRAVEL BAR ON THE MATANUSKA RIVER. ENGINE BEGAN RUNNING ROUGH AGAIN AND STARTED TO LOSE POWER. CARB HEAT WAS APPLIED BUT ENGINE CONTINUED TO LOSE POWER. ATTEMPTS TO FURTHER LEAN THE ENGINE DID NOT RESTORE POWER AND THE INSTRUCTOR DECIDED TO LAND ON A NEARBY SAND BAR. AIRCRAFT CAME TO THE END OF THE SAND BAR AND THE MAIN TIRES ROLLED INTO APPROXIMATELY 10 INCHES OF WATER WHICH CAUSED THE AIRCRAFT TO NOSE OVER COMING TO REST ON ITS BACK IN THE RIVER RESULTING IN A CRACKED WIND SCREEN AND A SMALL DENT TO THE TOP OF THE RUDDER. NO INJURIES TO OCCUPANTS.