Smoke lingers in the air in a cornfield in Bull Valley Monday after it moved into the area from the Canada wildfires. | Photo Submitted to Lake and McHenry County Scanner

Officials are urging sensitive groups to avoid outdoor physical activity due to wildfire smoke from Canada creating “very unhealthy” conditions in Lake and McHenry counties.

The U.S. Environmental Protection Agency’s AirNow, which reports air quality in the United States, reported poor air quality in the northern Illinois and Wisconsin area Monday.

Multiple data collection sensors in Lake County and McHenry County showed an air quality index of more than 151 as of Monday evening.

A reading of 151-199 means “unhealthy” and 201 and over means “very unhealthy,” according to AirNow.

The data collection sensors on Tuesday showed the air quality had worsened.

AirNow reported readings of over 201 in some areas of both counties, meaning “very unhealthy” air quality.

Federal officials recommend that older adults, people with heart or lung disease, pregnant women, children and teenagers avoid all outdoor physical activity.

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Smoke lingers in the air near railroad tracks in downtown Crystal Lake Monday after it moved into the area from the Canada wildfires. | Photo Submitted to Lake and McHenry County Scanner

Everyone else is recommended to limit their outdoor physical activity and go inside if symptoms occur.

Residents throughout the Chicagoland area first reported seeing the hazy smoke lingering Monday afternoon into the evening.

The National Weather Service (NWS) says the smoke seen in the Midwest is due to wildfires in Canada.

The weather service issued an air quality alert Tuesday morning for all of the Chicago area.

The NWS said the poor air quality will continue into Wednesday.

In addition to being cautious outdoors, residents are recommended to keep windows closed overnight and run their central air conditioning with furnace filters rated MERV-13 or greater.

Those who choose to wear a face covering should use a mask rated N95 or greater to be most effective at stopping fine fire particulates.