Miles of sea shores in Los Angeles were shut to swimmers Monday as 17 million gallons of sewage from the city’s biggest treatment plant spilled into Santa Monica Bay the prior night.

A mechanical disappointment “at the Hyperion plant last night made untreated sewage be released into the sea,” Los Angeles County Supervisor Janice Hahn said on Twitter. “Water tests are being tried and I’m getting more data about the extent of the issue. Sea shores from El Segundo to the Dockweiler RV Park are shut for swimming.”

Conclusion signs were posted in the spaces around El Segundo and Dockweiler State Beaches, just as Grand Ave. Tempest Drain, and authorities encouraged guests from going into the water. The sea shores, which in all out around four miles, will stay shut until water test tests come up negative for microscopic organisms, the County Department of Public Health said in a news discharge.

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The Hyperion plant is both the city’s biggest and most seasoned sewage treatment office and has been in activity since 1894. The plant was intended to oblige a day by day stream of 450 million gallons of water each day.

Chief Plant Manager Timeyin Dafeta said in an explanation that the office “became immersed with overpowering amounts of garbage, causing reinforcement of the headworks offices.”

“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.

About 6% of the facility’s daily load was discharged as an emergency measure to prevent the plant from going offline and spewing even more raw sewage, the statement said.