Surface conditions were; strong south-easterly winds of 30 knots with gusts to 40 knots, water surface choppy. The pilot made three unsuccessful attempts to align the aircraft for a takeoff. On his fourth attempt he was successful and the takeoff run was commenced. Shortly afterwards, a gust of wind lifted the left wing, the right float dug into the water, and the aircraft nosed over. Both occupants swam clear of the aircraft which had come to rest upside down on a submerged mudbank. The takeoff attempt had been made on the town reach of the river in a crosswind. An into-wind takeoff would have been possible if the pilot had taxied the aircraft to the next reach of the river.
