Nearly one million people in the Portland metro area depend on drinking water from the Bull Run Reservoir below Mount Hood.
The protected watershed includes 102 square miles of forested Cascade foothills -- a huge area that's hard to get to if you have to fight a wildfire.
"We do a lot in terms of prevention, detection and then planning for initial attack and suppression," said Liane Davis, the Portland Water Bureau's Bull Run watershed protection manager.
In 2017, the Eagle Creek fire grew so large that it burned into the very edge of land managed as part of the Bull Run watershed.
People aren't allowed into the watershed, which helps prevent human-caused fires.
As fire danger grows, Portland's water bureau will post a fire watch at strategic sites in the watershed and increase patrols for any small fires.