THE PILOT AND THREE PASSENGERS WERE DEPARTING FROM THE MOUTH OF A RIVER IN A FLOAT EQUIPPED AIRPLANE, TO RETURN THE PASSENGERS TO A FISHING LODGE. DURING THE TAKEOFF, THE AIRPLANE BECAME AIRBORNE, BUT STRUCK THE EDGE OF A 7 FOOT HIGH RIVER BANK. THE AIRPLANE SLID OVER THE BANK AND DOWN TOWARD AN OCEAN BEACH, THEN NOSED OVER. IT RECEIVED DAMAGE TO THE FLOATS, WINGS, FUSELAGE, AND VERTICAL STABILIZER.