The pilot reported that while taking off from Lady Musgrave lagoon, just after the aircraft became airborne, a gust of wind caused the right wing to drop. The wing contacted the water surface and the aircraft cartwheeled to the right. The windscreen was shattered and the cockpit filled with water immediately. The aircraft came to rest inverted under the floats in approximately 8 metres of water. The rear seat passengers egressed safely from the right side of the aircraft with cuts and bruises.The pilots door was jammed but the pilot kicked out the side window and egressed with the front seat passenger from the left side of the aircraft. The aircraft was eventually washed onto the reef and destroyed by wave and tide action. An attempt to salvage the aircraft was unsuccessful. The pilot reported that the wind at the time was a 20-25 knot south-easterly, the general weather was squally conditions with wind gusts to 30 knots, and the sea state was choppy with waves to one metre.