Canadian wildfires affecting parts of U.S.: What to know, where they are

Uncontrollable flames are ravaging swaths of Canadian forest in what authorities have described as a "devastating" wildfire season that could become the worst the country has ever seen.

The United States’ northern neighbor is home to some of the world's densest forests, and it experiences wildfires every year. But this year, the fires have been particularly widespread, numerous and intense, burning through millions of acres in Canada.

Live updates: Canadian wildfire smoke brings dangerous air pollution to U.S.

Canada's government expects "higher-than-normal fire activity" to continue throughout the wildfire season — which typically lasts between April and September — because of a combination of ongoing drought conditions and hot temperature forecasts.

Smoke and haze from the Canadian wildfires have also affected the United States, leading authorities from New York to Minnesota to issue public health alerts and urge people to stay indoors and wear masks to protect themselves from potentially toxic fine particles in the air.

Here's what you need to know.

Latest news: Smoke from Canadian wildfires is spreading south over much of the Midwest, Ohio Valley, Northeast and Mid-Atlantic, bringing dangerous air pollution to the United States. Follow live updates on the wildfires and the impact on air quality.

Where the wildfire smoke is the worst: Satellite imagery Tuesday evening showed smoke covering the Northeast and extending into the Carolinas. Air quality in New York City was particularly poor, and officials urged at-risk residents to wear high-quality masks outdoors. See photos from New York as smoke blankets the city.

Air Quality Index: The U.S. Air Quality Index is the EPA's index for measuring and reporting air quality. Here's an explanation of what Code Red, Code Purple and more mean and why wildfire smoke is so bad for you, plus how to protect yourself.