The pilot of the amphibious-float equipped airplane reported that, while departing from a lake, the floatplane was not "gaining airspeed as usual" and that the takeoff run was taking "longer." Prior to aborting the takeoff, the left float lifted off the water, followed shortly by the right float. While in ground effect, the floatplane started to roll to the right. He corrected with full left aileron, but the floatplane continued to roll to the right. He then reduced power and applied 40º of flaps and still the floatplane rolled right so he increased the throttle to full and the right wing impacted the water. The airplane sustained substantial damage to the right wing. Two witnesses reported that, about one hour prior to the accident flight, the same floatplane controlled by the same pilot, water taxied over rocks near the floatplane deck. The pilot added that the lake was 2 to 3 feet lower than normal and while water taxiing back to the floatplane deck, he saw the rocks but did not realize it caused any damage to the floats. After the flight, he did not find any residual water in the floats but did not examine the rest of the floats because it was under water.