On August 19, 2022, about 1700 eastern daylight time, a Piper PA-28-140, N587FL, was substantially damaged when it was involved in an accident near Marathon, Florida. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot stated that after takeoff, the airplane was not climbing as expected. The airplane was below 500 ft mean sea level (msl) when he elected to return to the airport. He stated that the engine sounded like it was “running fine,” but the airplane was “just not climbing.” About 300 to 400 ft msl the airplane sustained a total loss of engine power. The airplane’s wings began to wobble, and the pilot felt it was beginning to stall. He pitched down and, unable to reach the runway, he performed a forced landing to shallow salt water a mile north of the airport. Postaccident examination of the airplane revealed substantial damage to the wings and vertical stabilizer. The engine remained secured to the engine mounts and all engine accessories remained attached; salt water was present in the engine. About 7 quarts of oil and 1 quart of salt water were drained from the engine. Borescope inspection of the cylinders revealed saltwater corrosion was present in all cylinders. The fuel and oil lines were secure and fuel was drained from the gascolator bowl. The filter was free of debris and sand was present in the bowl. All eight spark plugs were removed and placed on a test bench; 4 were not functional (2T, 3T, 4T, and 4B). Three of the four nonfunctioning spark plugs were connected to the left magneto. When tested, the right magneto produced spark on all leads. The left magneto produced spark intermittently; it was disassembled and rotated manually to verify that all points were opening and closing. Four days before the accident, a 100-hour inspection was completed and noted “cleaned and gapped spark plugs.” The mechanical fuel pump functioned normally. The electric fuel pump filter was free of debris and contained AVGAS; no fuel was found in the lines from the fuel pump. The engine was rotated manually and thumb compression was obtained on all cylinders. Upon recovery, the fuel selector valve was found turned to the left tank, the magnetos were set to “Both,” and the ignition master switch was found ON. The electric fuel pump switch was found in the OFF position. According to the Pilot’s Operating Handbook the electric fuel pump should be ON for takeoff, landing, and loss of engine power inflight emergency procedure. The fuel mixture was found in the full rich setting and the throttle was set to the idle position. The year before this accident the pilot was involved in another accident involving a loss of power shortly after takeoff. After that accident in January 2021, he reported 200 total hours of flight experience. On the application for his most recent medical certificate, dated October 2021, he reported 211 total hours of flight experience. The pilot did not complete the NTSB 6120.1 or provide any documentation of his flight experience. The pilot stated his logbook and iPad were onboard and lost during the accident. The airplane remained submerged in saltwater until the next day when it was recovered. According to local law enforcement and Federal Aviation Administration officials, the pilot returned to the accident site after dark and after first responders had cleared the accident scene, and he dove down to recover his belongings from the submerged airplane.