The Detroit area woke up Wednesday to some of the worst air quality in the United States as smoke from Canada’s wildfires settled over the Great Lakes region and an unhealthy haze loomed. is spreading southward into Missouri and Kentucky.

The U.S. Environmental Protection Agency’s AirNow.gov site placed Detroit in the “danger” zone and warned that “everyone should stay indoors and reduce activity levels.”

Smoke from wildfires lowered haze curtains across large swaths of the country, moving into southern Illinois, Indiana and Ohio, and into parts of West Virginia. AirNow.gov listed air quality in Chicago, Indianapolis, Cleveland, Ohio on Wednesday; and Pittsburgh as “very unhealthy.” A wider circle of dirty air spread to St. Louis, Missouri, and Louisville, Kentucky.

“Another pass will pass through western New York and western Pennsylvania later today,” said Byran Jackson of the National Weather Service. “And then it continues into the northern Mid-Atlantic. “It will persist there until Thursday.”

“Air quality is particularly poor … in southern Wisconsin, Illinois, central Indiana and also in another area of ​​southeastern Michigan, Detroit and northeastern eastern Ohio, around Cleveland,” the meteorologist added. “This is particularly dense smoke.”

Chicago Mayor Brandon Johnson urged young people, the elderly and residents with health problems to spend more time indoors as poor environmental conditions persist.

In Canada, 490 fires are burning, and 255 of them are considered out of control.

Canada reported Monday that 76,129 square kilometers (29,393 square miles) of land, including forests, have burned across the country since January 1. Wet weather in Quebec gave firefighters some advantage, but there was not enough rain to put out the forest fires.

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Trisha Ahmed and Steve Karnowski in Minneapolis, Ken Kusmer in Indianapolis, Rebecca Reynolds in Louisville and Julie Walker in New York contributed to this report.