AFTER THE FLOAT EQUIPPED CESSNA TOUCHED DOWN ON A LAKE, A GUST OF WIND RAISED THE LEFT WING, ALLOWING THE RIGHT WING TO CATCH THE WATER AND CARTWHEEL THE AIRPLANE. THE PILOT REPORTED THAT THE GUST APPEARED TO HAVE COME FROM THE MOUTH OF A RIVER ADJOINING THE LAKE, AND THAT HE SHOULD HAVE TOUCHED DOWN BEFORE THE MOUTH OF THE RIVER.