Emergency crews were called to the Looking Glass River in Portland for a substance leaking into a the river.
It happened just after 2 p.m. Sunday afternoon near Two Rivers Park.
A man was cleaning paint brushes with a mixture of water and a petroleum based substance while working on the roof of the Looking Grand Cafe.
He poured the mixture down the roof drain and did not know it would drain directly into the river.
People at a restaurant nearby along the river could smell and see a substance floating down the river. That's when police were called.
A hazmat team was called to the scene to investigate.
A boom will remain in the river for 24 hours to soak up the substance. The Department of Environmental Quality will make an assessment of the incident.
Police estimate about a gallon of the substance made it into the river.
Crews have since cleared the area.