On April 11, 2013, about 1530 eastern daylight time, an experimental, amateur-built Searey amphibian airplane, N914WM, was substantially damaged during collision with water after departing controlled flight after takeoff from Lake Agnes, Polk City, Florida. The private pilot/owner reported a minor injuries and the passenger was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight, which was conducted under the provisions of 14 Code of Federal Regulations Part 91. The pilot described the performance of the airplane as "customary" and "normal" during taxi and takeoff from the surface of the lake. At an estimated 100 feet above the lake, the pilot heard a "loud bang or crashing sound." The airframe then twisted, and the airplane entered an uncontrolled, spiraling descent to water contact. The pilot held a private pilot certificate with ratings for airplane single-engine land, airplane single-engine sea, and instrument airplane. His most recent Federal Aviation Administration (FAA) second-class medical certificate was issued on October 25, 2011. The pilot reported 3,980 total hours of flight experience, of which 745 hours were in the accident airplane make and model. According to FAA records, the airplane was assembled in 2004 and was equipped with a Rotax 914 engine. The airplane's most recent conditional inspection was conducted on April 6, 2012. At the time of the accident, the airplane had accrued 880 total hours of operation. The current owner was issued an airworthiness certificate for the airplane in 2006, and a review of maintenance records and a pre-buy inspection revealed no previous damage or structural repairs. The airplane was recovered from the lake, and moved to the kit manufacturer's facility where it was examined under the supervision of an FAA aviation safety inspector. Examination of the airplane revealed that the right/forward wing strut attach bolts fractured. Examination of the bolts and their installation revealed that they were not the prescribed hardware, and had been installed at some point after the airplane's original assembly. The bolts were shorter than the prescribed bolts, had been installed opposite the prescribed direction, and had fractured in the threaded portion of the bolt. Further examination of the wreckage revealed that the inspection port for the right wing strut connection was covered during a previous, undocumented repair. The airplane builder stated he had seen photographs of the airplane damaged beneath a hurricane-collapsed hangar. The covering of the inspection port made it impossible for pilots or maintainers to inspect the connection and associated hardware. As a result of the investigation, the kit manufacturer posted four recommendations to owners on the Searey Technical website. The recommendations involved both specific technical and general maintenance practice advice for owners.