Canadian wildfire smoke returned to Wisconsin this weekend, with unhealthy levels for people with asthma and heart disease.

Unhealthy air has invaded Minnesota, Wisconsin and North Dakota early this week as a new round of wildfire smoke from Canada has wafted into the region, choking out areas as far south as Chicago and Detroit.

Smoke from wildfires in Manitoba, a Western province facing its worst fire season in 30 years, has created hazardous air quality conditions across Eastern Canada and the United States.