Smoke from dozens of intense wildfires burning across western Canada has drifted into the United States, prompting authorities in Colorado and Montana to issue air quality alerts.

The Colorado Department of Public Health and Environment has issued watches and advisories from Saturday afternoon through Sunday afternoon for much of the eastern half of the state, including Denver. He warned that the air quality can be unhealthy during this time.

“People with heart or lung disease, the elderly and children should not engage in prolonged or vigorous activity; Everyone else should reduce prolonged or heavy activity,” the department said.

Particle pollution sent the air quality index in parts of the Front Range soaring to 168 on Saturday, according to the department. A reading between 151 and 200 represents unsanitary conditions that may affect sensitive groups, as well as some members of the general public.

An air quality alert also went into effect Saturday in Montana, with the highest concentrations of smoke in the central and eastern parts of the state, according to the Department of Environmental Quality.

The Utah Department of Environmental Quality noted Friday that it was beginning to detect smoke on its monitors in northern and eastern portions of the state. He urged residents not to engage in outdoor activities in areas where there is visible smoke or haze.

The smoke created widespread haze in Idaho during the week, according to its Department of Environmental Quality.

The fires in Canada have burned mainly in the province of Alberta, where thousands of residents have been evacuated and regional authorities have issued state of emergency alerts. There have also been fires in British Columbia.

In Calgary and Edmonton, Alberta’s two largest cities, the Canadian government’s Air Quality and Health Index determined on Saturday that the health impact was ‘very high risk’ . Sensitive groups, such as children and the elderly, have been advised to avoid all physical activity outdoors.