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 land owners reminded to prepare properties for upcoming fire season
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'I am deeply sorry': WA Governor formally apologises over 1834 Pinjarra Massacre
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