Canada Wildfire Smoke Triggers Toronto and U.S. Air Quality Alerts

Smoke from hundreds of wildfires in Western Canada is wafting east, raising air pollution to hazardous levels across major Canadian cities like Toronto, as well as parts of the upper Midwest in the United States.

After a weekend of heat, hazy skies settled over Toronto, Canada’s largest city, on Monday, and officials at Environment Canada, a federal department, issued an air quality alert.

As of early Monday afternoon, Toronto’s air quality ranked among the worst around the world, according to IQAir, a global air monitoring platform.

Environment Canada advised residents to avoid rigorous outdoor activities in Toronto and most of the rest of Ontario, and issued the same warnings for Saskatoon, the largest city in the western province of Saskatchewan.

In the United States, the Great Lakes region has also seen reduced air quality, particularly in northern Minnesota and Wisconsin, western New York and northern Pennsylvania.

When wildfire smoke remains at atmospheric levels it doesn’t have a major impact on human health, but air quality worsens when the smoke is forced down toward the earth’s surface, said Ian Hubbard, a meteorologist at Environment Canada.

The air quality in Toronto is expected to improve overnight and into Tuesday, Mr. Hubbard said, though above-normal temperatures of over 30 degrees Celsius, or 86 degrees Fahrenheit, will persist for most of the week.

While Canada’s wildfire season has so far not been nearly as severe as 2023, when a record number of acres burned, the western province of Manitoba is having its worst season in about 30 years, the provincial government says.

Wab Kinew, Manitoba’s premier, declared a state of emergency for the second time last week — the first time was in May — to assist with deploying resources and evacuating people.

Two people were killed in a town northeast of Winnipeg, the provincial capital, in May, and more than 30,000 others were forced to evacuate their homes, including hundreds who were moved from remote areas by helicopters operating in dangerous conditions.

Wildfire smoke has emerged as another source of tension between the United States and Canada, which are already locked in a trade battle set off by President Trump’s tariffs.

Six Republican lawmakers in Wisconsin and Minnesota, in a public letter last week, blamed the Canadian government for the smoke blanketing their states.

Tom Tiffany, a Republican congressman from Wisconsin who signed the letter, took to social media over the weekend to again criticize the Canadian government.

“Canada owes us answers for its forest management failures,” Mr. Tiffany said in a post on X, sharing a video where he appears to be filming a smoky sky over a lake.

Many of Canada’s wildfires break out in remote areas that are not managed by forestry officials because they are not easily accessible. Lightning strikes are the leading cause of Canada’s wildfires.