The pilot reported that while on final approach to a remote gravel bar adjacent to a river, in gusty and variable wind conditions, the 10 knot headwind subsided just before touchdown, and the airplane descend below his anticipated approach path. He initiated a go-around, but the right wing abruptly dropped, and the right main wheel struck the water, which pivoted the airplane 90 degrees to the right. The airplane’s right wing subsequently struck the surface of the water, sustaining substantial damage. The pilot reported that there were no preaccident mechanical anomalies with the airplane.