On June 29, 2018, about 1307 Alaska daylight time, a float-equipped Piper PA-18 airplane, N7675D, sustained substantial damage when it was involved in an accident at Lake Hood Seaplane Base (LHD), Anchorage, Alaska. The pilot sustained minor injuries and the passenger was uninjured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot stated that he and the pilot-rated passenger fueled the airplane before the flight from his private fuel tank at his floatplane slip and that the preflight inspection and engine run-up were normal. The pilot was conducting a takeoff from the rear seat. During the initial climb from the north water lane, when the airplane was between about 100 and 200 ft above ground level (agl), the engine began to "sputter" and lose power. Realizing he would not be able to land on the water, the pilot turned the airplane to land on a nearby gravel runway and asked the passenger to check that the fuel selector valve was in the "on" position, and he responded that it was. He "pumped" the throttle to restore power to no avail. The airplane subsequently impacted the grassy area between the runway and a taxiway. The passenger statement corroborated the pilot’s statement, but he added that the airplane landed with a nose-high attitude and then banked right. The airplane then slid across a taxiway and another grassy area and sustained substantial damage to the fuselage and wings. The airplane came to rest on a heading of about 070°. Examination of the airplane revealed that it had sustained substantial damage to the fuselage and wings. At the accident site, a large amount of fuel was observed leaking from the left wing root. Examination of the pilot’s private fuel tank and system revealed that some debris was in the fuel nozzle, but no water or debris was found in a fuel sample taken from the nozzle. Postaccident examination of the engine and fuel system was conducted 2 months after the accident, during which time, the engine cowling was off, and the wreckage and engine were exposed to rain. The engine was attached to the airframe and intact, and the fuel and oil lines were secure. The fuel selector switch was found positioned to the “left fuel on” position. The propeller assembly remained connected to the engine crankshaft and could be rotated by hand. One propeller blade had a rearward curl and slight S bend at the outer 8 inches and exhibited leading edge impact damage and scrapes. The other blade was straight with extensive trailing edge impact damage and dirt and grass dried onto the cambered face. Corrosion and some carbon deposits were found around the spark plug threads, gasket, and neck. Spark could not be produced at the leads when the propeller was rotated. The magnetos were then bench tested with no anomalies noted. The propeller and crank shaft could be manually rotated, and crank case and valve train continuity was established. The fuel strainer was full of fuel, and minimal debris was present. The fuel line from the strainer to the engine and the carburetor had no fuel present, and no blockages were found. All fuel samples taken from the system and all system filters were clear of sizeable debris, consistent with avgas, and no water was found. No evidence of any preaccident mechanical malfunctions or failures were found that would have precluded normal engine operation.