On August 28, 1998, at 1800 hours Pacific daylight time, an experimental Mohr EAA Biplane P, N883TM, veered off grass runway 23 and came to rest inverted at the Frazier Lake Airpark, Hollister, California. The aircraft, operated under the provisions of 14 CFR Part 91, sustained substantial damage. The noncertificated private pilot/owner, the sole occupant, was not injured. Visual meteorological conditions existed at the time. One witness, a Federal Aviation Administration (FAA) designated pilot examiner, stated that the grass strip is located adjacent to a lake that is used for water landings. He stated that after the aircraft landed it departed the left side, went into the water, and came to rest inverted. Witnesses to the accident reported that the winds were approximately 90 degrees to the runway at 20 knots. They further stated that the landing was normal, but on the landing rollout the pilot lost directional control of the aircraft. Witness stated that the pilot attempted to conduct a go-around, but ground looped the aircraft. Review of the pilot's FAA Airman Certification file disclosed that his private pilot certificate was revoked on October 25, 1988, and his medical certificate was revoked on October 12, 1988. The accident was reported to the Safety Board on September 9, 1998. The location of the aircraft is unknown at this time. The pilot/owner was given a Pilot/Operator's Report Form 6120.1/2, and a copy was sent by certified mail to him with no response.