PORTLAND, Ore. (AP) — The City of Portland is working to clean up and contain an oil sheen on the Columbia Slough caused by illegal dumping.

The Portland Bureau of Environmental Services said containers with a mixture of oil and gas discovered around midnight Sunday were dumped on the roadway above the slough near Alderwood Road.

City contractors placed booms in the water to contain and absorb the fluid. Environmental Services advises people recreating on the slough to avoid the immediate area around the NE Glass Plant Road bridge.

Each container holds a maximum of 275 gallons but only a fraction of that amount is believed to have reached the slough. Portland Fire & Rescue and Portland Bureau of Transportation managed the initial response and cleaned up the residue on the roadway.

Anyone with information about this incident is asked to call Environmental Services’ spill response hotline at 503-823-7180.