The pilot of the float-equipped airplane reported that, during approach to land on a lake, he aligned the airplane based on wind indications on the water as well as observing other seaplanes. After the water landing, while slowing and coming off the step, a wind gust lifted the right wing, the left float dug into the water, and the airplane nosed over. The pilot and pilot rated owner egressed and were rescued by boaters. 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 pilot reported that the wind was from 090° at 10 knots, gusting to 15 knots. A weather station, located about 8 miles to the southwest of the accident site, about the time of the accident, reported temperature 63°F, dew point 46°F, and wind from 185° at 7.8 mph, gusting to 10.3 mph.