On takeoff from Miho the co-pilot found the elevator control too heavy to rotate and aborted the takeoff. The aircraft could not be stopped on the runway and overran runway 25 (1500 m long) by 60 m, ending up in shallow water. The aircraft had not been de-iced. With light snow showers, ice or slush might have affected elevator control. Also, the captain had been acting as such on YS-11 aircraft less then 6 months; he was not allowed to leave the controls to the co-pilot during takeoff. It is presumed that this accident occurred because the aircraft failed to stop by the overrun zone after the takeoff abort maneuver was performed at a high speed exceeding takeoff runway speed V2. The co-pilot aborted the takeoff because he felt the elevator rudder was too heavy and judged that he could not cause the aircraft to take off by steering the elevator rudder. This may be related to the fact that no anti-icing work was performed on the aircraft. The failure to stop on the runway may have been caused by the high speed at which the aircraft aborted takeoff, slush on the runway surface, and reduced braking effect due to the small weight of the main landing gear.