Detectives are trying to identifying a group of men who were involved in a New Year's Eve altercation that left a 50-year-old man in hospital.
The group of men were camping near the ski boat ramp at the Glen Mervyn dam near Mumballup.
Throughout the day were seen using a gold ski boat with what is though to be a large Mercury V6 outboard motor.
It is believed they were involved in a race with a white coloured speedboat.
Just before 7pm, the victim took his boat out and a verbal altercation took place with the group before the man returned to his campsite without competing in the race.
About 7.30pm a light coloured F100 utility was travelled through the campsite with about six men in the tray.
Another verbal altercation took place between the victim and the offender that resulted in a punch being thrown. The victim fell to the ground unconscious.
The group then fled the scene.
The victim was taken to Bunbury Regional Hospital by his partner and transferred to Fremantle Hospital where he remains in a stable but serious condition.
He is being treated for a fractured jaw and nose, and a suspected skull fracture.
The offender has been described as 20-30 years old with fair skin, short, light, curly hair, about 180cm tall and of a solid build with tattoo sleeves on his arm.
Anyone with information about the attack is asked to call either South West Detectives on 9722 2005 or Crime Stoppers on 1800 333 000.