According to the pilot, he intended to fly the float-equipped airplane for approximately one hour to practice for his airplane sea rating. During the flight, the engine lost 100 revolutions per minute (RPMs) on four or five different occasions. At 1,000 feet above ground level, the engine sputtered and lost power. The pilot executed a forced landing to a field. During the landing, the airplane impacted terrain and nosed over. Examination of the airplane revealed the fuselage was buckled. A postaccident inspection and test run of the engine failed to reveal any mechanical anomalies. The nearest weather reporting facility, located 10 nautical miles southwest of the accident site, recorded a temperature of 22 degrees Celsius (C) and a dew point of 18 degrees C at the time of the accident. Review of the carburetor ice probability chart revealed that the temperature and dew point were conducive to serious icing conditions at glide power. The airplane was equipped with carburetor heat, but the pilot stated that he did not use it. The pilot reported a total of 1,859 flight hours and 12 flight hours in the accident airplane.