On August 25, 2007, about 1330 Alaska daylight time, a float-equipped Cessna 150G airplane, N2981S, sustained substantial damage when it ran aground and nosed over, during an aborted takeoff at the Kenai Municipal Seaplane Lake, Kenai, Alaska. The airplane was being operated by the pilot as a visual flight rules (VFR) personal local flight under Title 14, CFR Part 91, when the accident occurred. The private certificated pilot and sole passenger were not injured. Visual meteorological conditions prevailed, and no flight plan was filed. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on August 25, the pilot said during the takeoff roll the airplane did not accelerate as fast as normal, and once on step did not accelerate as anticipated. He said he aborted the takeoff, but the airplane was not going to stop in the remaining length of the lake. The pilot said he elected to hit the bank head-on rather than in a turn, attempting to avoid the shore. He said the airplane had slowed considerably, but traveled onshore 20-30 feet before nosing over. He said when he exited the inverted airplane, the left float was draining what he thought was an excessive amount of water. He said he pumped the floats prior to departure, but felt that a leaking gasket may have filled the left float with water during the pretakeoff water taxi. On August 30, the FAA air safety inspector who interviewed the pilot, told the IIC the pilot told him he had inadvertently left the flaps in the 40 degrees extended position during the takeoff roll. The airplane was not examined by the NTSB. The pilot did not complete the NTSB form 6120.1 Pilot/Operator Aircraft Accident/Incident Report as requested.