THE FLOAT EQUIPPED CESSNA 180 AIRPLANE FLIPPED OVER WHILE LANDING NEAR GREEN ISLAND, AK. THE AIR TAXI PILOT WAS FLYING TWO BOAT CREW MEMBERS TO THEIR BOATS ON AN UNSCHEDULED CHARTER FLIGHT. WITNESSES STATED THAT THE AIRPLANE APPEARED TO BE FLARING TO LAND, WHEN IT ENTERED A SLIGHT LEFT TURN & THE LEFT FLOAT 'DUG INTO' THE WATER. THE PILOT BELIEVED THE AIRPLANE MAY HAVE ENCOUNTERED A BOAT'S WAKE THAT HE DID NOT SEE BEFORE THE ENCOUNTER. A CREW MEMBER FROM A NEARBY BOAT DOVE INTO THE WATER AND HELPED THE PILOT AND PASSENGERS ESCAPE.