(NEXSTAR) – Canadian wildfires are contributing to worsening air quality in dozens of U.S. cities and towns this week, officials say, with states along the northern border currently experiencing the brunt of the pollution.

Parts of the upper Midwest and westward toward the Rockies, including Iowa, Montana, North Dakota, South Dakota and Wisconsin, are seeing the worst dips in air quality Monday morning, according to the EPA-affiliated U.S. Air Quality Index (AQI). The unhealthiest air, however, is currently recorded in Minnesota, where the Twin Cities metro and surrounding areas under a state air quality alert.

As of Monday morning, the air quality in nearly the entire southern half of the state was shown to be “unhealthy” or “unhealthy for sensitive groups,” per the Minnesota Pollution Control Agency.

Still, Minnesota’s overall air quality is an improvement over Sunday, when the entire state was expected to experience “unhealthy” air, officials wrote.

Air categorized as “unhealthy” also lingered over Wisconsin as of Monday morning, according to the AQI, though Wisconsin officials expected the air to improve in the coming days, before once again dipping Wednesday into Thursday.

A map of the air quality across the U.S. showed mostly moderate air quality in the Dakotas, eastern Montana and northern Iowa as of Monday.

Dozens of wildfires are currently contributing to worsening air quality in the region, with some of the most intense burning in British Columbia, Alberta and Saskatchewan, according to the Canadian Wildland Fire Information System.

One of the fires, burning in Fort Nelson, B.C., is actually a holdover or “zombie” fire from 2023, never having fully been extinguished, the Canadian Broadcasting Corporation confirmed.

Officials in Canada added that the fires — and the unhealthy air quality they cause — are only expected to worsen with climate change.

“Some communities across Canada regularly experience wildfire smoke events,” reads a message from the Canadian health department. “This is expected to continue as Canada’s changing climate provides ideal conditions for more frequent wildfires and longer wildfire seasons.

“Wildfire season typically runs from early April to late October,” the agency added.

U.S. agencies have warned those living in areas with “unhealthy” or “unhealthy for sensitive groups” AQI levels should limit their time outside.

“Fine particles are respiratory irritants, and exposures to high concentrations can cause persistent coughing, phlegm, wheezing, and difficulty breathing,” the EPA warns. “Even in healthy people, exposures to fine particles can potentially lead to transient reductions in lung function, and pulmonary inflammation.”