Last week, Canadian wildfire smoke blanketed Wisconsin and caused the Air Quality Index to reach the unhealthy level for sensitive groups. Six days later, on July 31, the smoke appears to have a worse impact on the air.

Canadian wildfires in Manitoba and Saskatchewan have prompted air quality alerts in Minnesota, Wisconsin and Michigan on Wednesday and Thursday as residents are advised to "limit prolonged or heavy exertion.

It expires on Friday at midnight, due to elevated levels of fine particulate (PM2.5), the Department of Environment, Great Lakes, and Energy said.