The pilot reported that after landing the float-equipped airplane in the water, and while on the step with a 7 to 10 knot, 45 to 50 degree left crosswind, the wind "sheared" to a [left] quartering tailwind. After veering to the left the pilot applied "strong" right rudder to counter the left yaw. The airplane's right wing tip subsequently struck the water, which resulted in substantial damage to the right wing and right aileron.