On September 11, 1995, at 1900 Alaska daylight time, a float equipped Piper PA-18-150 airplane, registered to and operated by the pilot, struck a submerged object, collapsed the left float, and dragged the left wing, during step taxi for takeoff. The personal flight, operating under 14 CFR Part 91, was departing an unnamed lake located 30 miles on the 160 degree radial of the Big Delta VORTAC. The destination was Birch Lake located 7 miles away from the departure point. No flight plan was filed and visual meteorological conditions prevailed. The airline transport certificated pilot, the sole occupant, was not injured and the airplane was substantially damaged. During a telephone conversation with the pilot on September 26, 1995, he stated that the lake was small and he was step taxiing close to shore to gain as much takeoff area as possible. He felt the left float bump something. The nose of the left float than came up and bent the left wing struts and the airplane's left wing struck the water. The airplane stopped in 3 feet of water. The pilot stated that the float's wire braces and float struts were broken. He stated he was sure that the left float struck the bottom of the lake or a submerged object. He did not see any objects floating on the water prior to step taxiing.