The release of about 17 million gallons of untreated sewage from the city of Los Angeles’ largest treatment plant closed miles of beaches to swimming from the LAX area to El Segundo Monday, officials said.

A power outage Sunday night caused sewage from the Hyperion Water Reclamation Plant in Playa del Rey to spill into the ocean, L.A. County Supervisor Janice Hahn said in a tweet.

Officials say the unfiltered sewage was discharged into the Pacific through pipes that extend 1 mile and 5 miles offshore.

The facility “became inundated with overwhelming quantities of debris, causing backup of the headworks facilities,” Hyperion Executive Plant Manager Timeyin Dafeta said in a statement to the Associated Press.

“The plant’s relief system was triggered and sewage flows were controlled through use of the plant’s one-mile outfall and discharge of untreated sewage into Santa Monica Bay,” Dafeta said.

Hahn tweeted that officials are “going to need answers about how and why this happened.”

Beaches from the LAX area to El Segundo reopened to swimmers two days after a spill of about 17 million gallons of untreated sewage from the city of Los Angeles’ largest treatment plant closed miles of shoreline, officials announced Wednesday.