The Illinois Environmental Protection Agency has issued an air quality alert in effect for the entire state for the rest of the weekend.

The alert is in effect through Sunday night as smoke from Canadian wildfires again moves toward Illinois.

The smoke was expected to begin sweeping through Illinois from the northwest Saturday afternoon, according to the National Weather Service.

Those who are sensitive to poor air quality or have a chronic respiratory issues should limit outdoor activity, the weather service said. 

The wildfire smoke brings a toxic brew of microscopic contaminants known as “particulate matter 2.5.” Wearing N-95 or KN-95 masks can help filter out the dangerous pollution. 

The smoke from the wildfires made the air quality in Chicago “very unhealthy” June 27-28. On June 27, Chicago had the worst air quality among big cities in the world.