The pilot of the float-equipped airplane reported that, during takeoff on a tower controlled waterway in gusting crosswind conditions, he felt the wind direction shift as the airplane started to lift off. He added that a strong gust of wind then lifted the left wing, and the right wing dipped and impacted the water. He reduced power and shut the engine off. The impact had damaged the float connecting rod. The airplane came to rest upright on both floats, but the left float then separated from the fuselage, and the airplane sank. The airplane sustained substantial damage to the left wing lift strut. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation. The automated weather observation system about 1 nautical mile from the accident site reported that, about the time of the accident, the wind was from 170° at 7 knots with thunderstorms in the vicinity. According to the pilot, the tower had reported the possibility of gusts up to 20 knots. The pilot was departing the waterway to the east/southeast.