The environment ministry and Northern Health have issued an air quality advisory for Smithers due to pollution levels.
Officials say high concentrations of fine particulate matter are behind the advisory.
People with chronic health conditions should postpone strenuous exercise until the air clears and the advisory is lifted. Exposure to fine particulates is a particular concern for infants, the elderly, and those with diabetes, heart, or lung disease.
The use of wood stoves in Smithers is banned during air quality advisories unless it is the sole source of heat.
High concentrations are expected to continue until sometime Saturday.