Swimmers are warned to avoid a stretch of the Willamette River because of sewage contamination.

The sewage was discharged from the treatment plant near Lake Oswego’s Foothills Park.

Portland Bureau of Environmental Services says treated sewage that was not disinfected was discharged into the river overnight.

An estimated 500,000 gallons were released into the river without disinfectant.

The bureau says people should avoid the area for 48 hours after the incident.