Air will likely be unhealthy in the Central Valley for the next few days as the Junction Fire burns in Madera County.
Authorities say the smoke has triggered an air alert for at least five counties.
Since its start on Monday in Oakhurst, the Junction Fire has spread quickly.
It continues to threaten homes and pollute the air in surrounding counties including Stanislaus, Merced, Madera, Tulare, and Kings.
Anthony Presto with the San Joaquin Valley Air Pollution Control District says the smoke coupled with the hot days will pose a double danger.
"So what often happens during the summertime wildfires is not only do we get impacts from particulate matter which is the smoke, it's also generating the fuel to create ozone pollution," says Presto.
Presto says those most affected will be the elderly, young children, and people with respiratory conditions such as asthma, bronchitis, and emphysema.
Updates: Cal Fire and Madera County Sheriff's Office