(CNN)A stretch of Los Angeles beaches was closed due to health concerns after roughly 17 million gallons of sewage was discharged into the Santa Monica Bay.
The spill came from the Hyperion Water Reclamation plant, which is located next to Dockweiler State Beach and is the city's oldest and largest wastewater plant, operating since 1894.
Officials said they are investigating the cause of the incident on Sunday and have notified the state office of emergency services.
The spill prompted the closure of a one- to two-mile stretch of beaches near Los Angeles International Airport.
"Beaches from El Segundo to the Dockweiler RV Park are closed for swimming," L.A. County Supervisor Janice Hahn said Monday afternoon in a post on Twitter.
The Los Angeles County Department of Public Health said the beaches would remain closed until samples showed there was no longer elevated bacteria in the water. The results would be available within 24 hours, it said.
The sewage was released over an eight-hour period as an emergency measure "to prevent the plant from going completely offline and discharging much more raw sewage," the L.A. Sanitation and Environment department said in a statement.
On Sunday, the plant "became inundated with overwhelming quantities of debris," causing a backup in the facility, the department said. The plant's relief system was triggered, the statement said, and sewage flows were controlled through the plant's one-mile outfall and discharged into Santa Monica Bay.
Approximately 6% of the daily amount of sewage was discharged into the bay, the statement said.
The issue was resolved early Monday, and officials are conducting water-quality testing, the statement said.
"At this time, all flow is being treated through its standard treatment processes," the sanitation department said.