Directly from the Marysville Fire Department's press release:
As of Wednesday afternoon, Marysville firefighters are working to extinguish an illegal land-clearing burn in the 4800 block of 140th St NW. This fire could continue to smolder throughout the afternoon and evening, creating smoke in the area.
The fire was first reported at approximately 10:40 a.m. Wednesday morning. Firefighters will remain at the scene until the fire, consisting of three debris piles, is fully out. Currently, the risk of the fire spreading is extremely low. The Snohomish County Fire Marshal’s Office is also at the scene assisting.
Land-clearing burning is permanently banned in Snohomish County by the Puget Sound Clean Air Agency. The ban applies to fires used to clear land for development. It is also illegal to burn trash, use a burn barrel, or burn yard waste in urbanized areas.