OREGON CITY, Ore. -- A power outage at a wastewater treatment plant caused raw sewage to be discharged into the Willamette River on Sunday.

The outage began at 11:19 a.m. and continued through the afternoon.

About 3 million gallons of sewage has been dumped into the river so far, said Clackamas County officials.

The outage affected Tri-City Water Pollution Control Plant, which serves the cities of West Linn, Oregon City and Gladstone.

Signs have been posted in the area to inform the public about the sewage spill.

No sewage has leaked onto land and all of it has been discharged through piping into the river, officials said.

The cause of the outage is unknown but Portland General Electric crews were working to restore power Sunday.