The Wisconsin Department of Natural Resources is encouraging people with asthma, heart disease and other heart or respiratory ailments to limit or avoid outdoor physical activity after issuing an air quality alert Tuesday. The alert, which remains in effect until noon Thursday, covers Brown, Calumet, Door, Florence, Forest, Kewaunee, Langlade, Lincoln, Manitowoc, Marathon, Marinette, Menominee, Oconto, Oneida, Outagamie, Portage, Shawano, Sheboygan, Vilas, Waupaca, Waushara, Winnebago and Wood counties.

The heaviest smoke impacts, including the potential for hazardous (maroon) air quality levels, are expected across northwest Wisconsin, though higher smoke concentrations could also occur in communities near Lake Michigan.

The culprit is smoke from Canadian wildfires, which has already forced the closure and evacuation of the Boundary Waters Canoe Area Wilderness in northeastern Minnesota through at least Friday. The DNR also left open the possibility of extending the air quality alert beyond Thursday.

If you have asthma, follow your asthma action plan. People experiencing symptoms such as heart palpitations, shortness of breath or unusual fatigue should contact their health care provider.