Residents in the Shire of Toodyay, Northam and Mundaring have been advised to shut their doors and windows to reduce their exposure to smoke from a burn off in the area.
The Department of Biodiversity, Conservation and Attractions issued a smoke alert in the area just before 3pm on Tuesday.
The smoke is the result of a prescribed burn being carried out in Julimar State Forest.
It is expected to clear overnight.
WHAT TO DO:
If the smoke is particularly thick, it is recommended people shut doors and windows and turn off air-conditioners.
Smoke may reduce visibility on some roads and motorists should take care, turn on headlights and travel at appropriate speeds when travelling in these areas.
People with asthma and pre-existing respiratory or cardiovascular illnesses should follow their pre-prepared treatment plan.
People with conditions exacerbated by smoke should take precautions in line with their medical advice for these circumstances.