Residents of Portland, Oregon, have been advised to avoid one of the nation's largest rivers after roughly half a million gallons of sewage leaked into the water system, local officials said Monday afternoon. The reason for the advisory, officials said, is because there could be "increased bacteria" in the water. 

The issue is in the Willamette River, which according to nonprofit organization Willamette Riverkeeper is the 13th largest river by volume in the U.S. The river is also home to the nation's second-largest waterfall by volume and flows through some of the state's biggest cities, including Portland, Eugene and Salem. 

The mishap itself happened near Lake Oswego's Foothills Park, which sits along the river, officials said, when wastewater from the Tryon Creek Wastewater Treatment Plant suffered a "malfunction." The park sits right next to the wastewater treatment facility. 

"The wastewater had undergone all stages of treatment except the final one – the addition of a disinfectant," Portland's Bureau of Environmental Services said in its advisory on Monday afternoon. "A pump that delivers disinfectant failed around midnight and was repaired by 5:30 a.m." 

The volume of wastewater that then seeped from the plant was just a third of its normal flow, they added, but it's estimated that 500,000 gallons of the water was released into the river without the disinfectant. That stage of the process entails using sodium hyphochlorite to kill bacteria that may be remaining from the rest of the process, the Portland government says. 

The public has been advised to "avoid the river" around Foothills Park for 48 hours "due [to] the possibility of increased bacteria in the water," officials said. 

The wastewater treatment plant is nearly half a century old, and according to the city of Lake Oswego is "in need of major upgrades to continue to reliably meet Oregon Department of Environmental Quality water quality requirements." The city has been exploring the possibility of building a "new, resilient, and state-of-the-art" facility to replace it as it continues to age.  

In:
• Water Safety
• Environment
• Oregon

Li Cohen

Li Cohen is a social media producer and trending content writer for CBS News.