On March 11, 1997, approximately 1830 Pacific standard time, the pilot of a Gulfstream American AA-5A, N26848, ditched his aircraft in the waters of Coos Bay, near North Bend, Oregon. The instrument rated private pilot was not injured, but the aircraft sustained substantial damage. The 14 CFR Part 91 personal pleasure flight, which departed North Bend Municipal Airport about 10 minutes earlier, was en route to Yolo County Airport, California at the time of the accident. The pilot was on an IFR flight plan, and had received a weather briefing prior to departure. According to the pilot, after departing North Bend Airport, he was in visual meteorological conditions until entering clouds about 3,000 feet MSL. As the aircraft climbed through 6,000 feet, it began to pick up structural ice, followed by a significant reduction in engine power. Being unable to climb, or even maintain his present altitude, the pilot elected to return to North Bend Airport. Although the pilot tried to reach the airport, the loss of power caused him to execute an emergency landing in the waters of Coos Bay. A review of the audio tape of the weather briefing the pilot received from the flight service station prior to departure revealed that the freezing-level was forecast to be around 6,000 feet or a little lower, and that moderate rime or mixed icing was forecast in the clouds and precipitation. The briefer also informed the pilot that an aircraft which departed out of North Bend prior to the time of the briefing had reported the tops of the overcast at 12,000 to 13,000 feet. During a post-accident interview with an FAA inspector, the pilot stated that he had not used carburetor heat during the climb.