Northern Health and the environment ministry have issued an air quality advisory for the Smithers and Houston area.
Officials say high levels of fine particulates have developed because of an inversion and calm wind conditions.
The advisory says wood smoke is a major contributing pollutant to fine particulates in the Bulkley Valley.
The bulletin recommends avoiding strenuous activities and staying indoors in order to reduce exposure.
those with chronic underlying health conditions should postpone strenuous exercise until the advisory is lifted.