In the upper Midwest of the United States, Michigan, Wisconsin and Minnesota have issued air quality warnings as smoke from the Prairie wildfires is dragged south by a cold front. Those warnings expanded into the Northeast, causing some hazy skies.

Smoke from wildfires in Canada has spread more than 5,000 miles, reaching parts of Russia and Europe during the past week.

While the smoke may cloud your vision of the sky or ruin a day at the beach on this week's warmest days of the season so far, it is more than just a nuisance. All across the U.S., the smoke is causing poor air quality, which can cause health effects from mild symptoms in the healthy to dangerous risks for sensitive groups.