Officials say the Eagle Creek Fire entered the Bull Run watershed Tuesday.
The watershed provides drinking water for around 1 million Oregonians.
“At this time, the fire is not near the drinking water reservoirs or water supply infrastructure,” said Jaymee Cuti, public information officer for the Portland Water Bureau.
The watershed is on 100 square miles of protected federal forest south of the Columbia River Gorge. It is the primary source of drinking water for Portland and many of its largest suburbs, including Gresham and Beaverton.