Smoke from wildfires blazing across Canada is once again wafting over huge portions of the U.S. Midwest and worsening air quality there. On August 1 conditions are particularly bad in Minnesota, Iowa and Illinois.

The smoke is expected to remain over the northern and central Plains of the United States for the next couple of days, according to meteorologists.

The state of Minnesota is entering another in a long string of summer days marred by air quality alerts. Poor air quality will continue through Saturday with lingering wildfire smoke from Canada.