On July 4, 2004, about 1600 eastern daylight time, a Cessna 182Q, N6550F, was substantially damaged while ditching, following a partial loss of engine power near Brighton Beach, New York. The certificated commercial pilot was not injured. Visual meteorological conditions prevailed for the flight that departed Lakewood Airport, Lakewood, New Jersey; destined for Francis S Gabreski Airport, Westhampton Beach, New York. No flight plan was filed for the commercial banner tow flight conducted under 14 CFR Part 91. The pilot reported that he was towing a banner approximately 300 feet above the water near the shore. The airplane engine began to run rough, vibrate, and the pilot noticed a decrease in oil pressure. The pilot then released the banner and attempted to fly to Floyd Bennett Field. He turned the carburetor heat on, and positioned the throttle, mixture, and propeller levers full forward. The pilot also moved the fuel selector from "BOTH" to "LEFT," and "RIGHT," and back to "BOTH." However, the engine continued to run rough. The pilot was unable to maintain altitude, and ditched in Jamaica Bay. Following the ditching, the pilot exited the airplane before it sank. The pilot further stated that he did not attempt a landing on the beach because it was heavily populated. The pilot believed the loss of engine power was related to the mechanical vibration within the engine. The airplane had accumulated approximately 30 hours of operation, since the last annual inspection performed on January 6, 2004. A Federal Aviation Administration (FAA) inspector reported that the airplane was recovered, but the engine was not located.