Millions of people from the Great Lakes to the East Coast are breathing hazy air this week, and the source is hundreds of miles away.

Thick smoke from dozens of wildfires burning across Ontario and northern Minnesota is streaming into the U.S., pushing poor air quality into the Midwest, Northeast and Mid-Atlantic for an estimated 100 million people through the end of the week.

Air quality alerts are in place across several Great Lakes states, and cities like Boston, New York, and Philadelphia have seen skies turn a milky white or even yellow-brown in spots as the smoke settles closer to the ground.

The smoke is billowing from more than 50 active wildfires across Canada, with over a dozen new fires breaking out just this week. A shift in the jet stream is funneling that smoke straight into the Lower 48.

The Show-Me state isn’t under the same kind of alert New England is dealing with right now, but we’re not walled off from it either. This is the same setup that’s brought hazy Midwest skies in past summers when Canadian smoke rides the jet stream south.

It’s worth keeping an eye on air quality forecasts here over the next few days, especially for anyone with asthma or other breathing issues. Air quality sensors in metro areas in Kansas City and St. Louis are reporting moderate levels of air quality, meaning people with those sensitivities could be affected.

Wherever the smoke settles, make sure to limit time outdoors, especially strenuous activity, and pay attention to your local air quality index before you head out.