Main Roads has issued the warning along with advice for motorists this morning.
The fog is expected to be worst between Thomas Road and Mortimer Road in both directions.
Motorists are urged to turn on headlights and keep a safe breaking distance between other cars.
Extra travel time should also be taking into account due to reduced visibility.
Mandurah woman wanted for questioning over current investigation
Mandurah Police are urgently looking for a 35-year-old woman who is wanted for questioning over a current investigation.
Investigation underway into Bunbury sexual assault
Detectives are continuing their investigation into the alleged sexual assault of a 17-year-old girl in Bunbury.
Two motorcyclists seriously injured in separate crashes
Two motorcyclists have suffered serious injuries in separate crashes in Perth and the South West.
Miraculous escape for two men after plane goes down south of Mandurah
Two men have miraculously survived a plane crash south of Mandurah.
Baldivis family left devastated after rescue shelter takes back adopted dog due to breach of contract
A Baldivis family have been left devastated, claiming their dog Oakley was taken off them from the rescue shelter they adopted him from because he was sleeping outside.
Fire crews battle blaze at Baldivis Bunnings
Firefighters have extinguished a fire at Bunnings in Baldivis.
Claims now open for WA student payments
Financial support is now on offer to all Western Australian families with school-aged children.
Two people charged over South West murder
Two people have been charged with the alleged murder of a woman near Busselton.
Arson Squad to investigate Warnbro house fire
A house has been destroyed by fire in Warnbro.