On April 23, 2013, approximately 1000 eastern daylight time, a float-equipped Piper PA-18-135, N18JP, was substantially damaged during a forced landing near Inlet, New York. The certificated commercial pilot was seriously injured. Visual meteorological conditions prevailed, and no flight plan was filed for the local personal flight, which was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. The pilot stated that a preflight inspection revealed no anomalies, and he departed Seventh Lake Seaplane Base (NK15) to the north, before turning the airplane west towards a nearby lake. He reported that shortly after turning west, the engine began to run rough and produce "surges of power." The pilot turned the airplane back towards Seventh Lake, but realized the airplane's airspeed and altitude were insufficient to clear trees on the shore. While attempting to maneuver the airplane between trees, the airplane experienced an aerodynamic stall and came to rest inverted on the shore of the lake in between 8-12 inches of water. The airplane was manufactured in 1953, and was equipped with a Lycoming O-320-A2B, 150-hp reciprocating engine. The airplane's most recent annual inspection was completed on June 6, 2012. The pilot held a commercial pilot certificate with ratings for airplane single engine land and sea, and instrument airplane. He reported 9,000 hours total flight experience, of which 600 hours were in the accident airplane make and model. Prior to the recovery from the lake, 6 gallons of fuel was drained from the left wing tank. The right wing tank was breached during impact. The airplane was then moved to the owners' hangar for further examination. The engine crankshaft was rotated at the propeller, and compression was obtained on all cylinders. The magnetos produced spark at their terminal leads. The carburetor was intact, and when opened, the float bowl contained a mixture of fuel and water. The 0953 weather observation at Griffiss International Airport (RME), located approximately 42 miles southwest of the accident site, included wind from 140 degrees at 12 knots, clear skies, 10 miles visibility, temperature 7 degrees C, dew point -3 degrees C, and an altimeter setting of 30.37 inches of mercury. Review of a carburetor icing probability chart published by the Federal Aviation Administration showed that the temperature/dewpoint conditions were favorable to the accumulation of ice at glide and cruise power.