Information supplied by the pilot and the operator indicated that the pilot landed at the strip, without problems, on the day prior to the occurrence. On the day of the occurrence she decided to fly the aircraft to a longer strip so that she could refuel and depart, with the planned load, for Bunbury. The pilot decided to carry a passenger for the short flight. Although the strip was 730 metres long the pilot decided to use only the last 600 metres. The strip was partially covered with bush, in places, up to 1.8 metres in height. The density altitude at the time of takeoff was approximately 4,000 feet. In order to avoid rough parts of the strip the pilot elected to fly the aircraft off the ground at 55 knots and allow it to accelerate in ground effect before climbing away. Shortly after lift-off the airspeed reduced to 40 knots and the aircraft did not accelerate. The pilot decided to reject the takeoff and the aircraft touched down with 150 metres to run to the end of the strip. Although the pilot applied heavy braking the aircraft overran the strip and collided with a fence and trees. Skid marks extended from the touchdown point to where the aircraft stopped (250 m). There were no indications that engine power was a factor in the occurrence. The Pilots Operating Handbook indicated that between 800 (short dry grass) and 1050 metres (long wet grass) of runway was required to reach a height of 50 feet above ground level in the prevailing conditions and using a takeoff safety speed of 56 knots.