Portland fire officials say that the juvenile identified as being responsible for a 20-acre fire on Government Island last week had set off an illegal firework.
The unnamed juvenile and parents are cooperating with the investigation into the Aug. 19 blaze, according to Portland Fire & Rescue.
Eighty firefighters, including some units from Vancouver Fire Department, battled the three-alarm blaze for more than five hours. Smoke from the fire could be seen for miles and at one point fire officials closed a portion of the Interstate 205 bridge over the Columbia River.
Oregon law bans possession, use or sale of any fireworks that fly, explode, travel more than one foot in the air and more than six feet on the ground.