The heavy rainfall caused an overflow which spilled 250,000 gallons of sewage into the Los Angeles River near Studio City.
People are being told to stay out of the water because the bacteria can cause illness.
The recent rains also triggered another sewage spill in Ventura County, where 10,000 gallons of waste water was discharged from Hill Canyon Treatment Plant into the Arroyo Conejo Creek on Monday.
There was also a 375 gallon sewage discharge in Thousand Oaks from a Triunfo Sanitation District manhole.
The Associated Press contributed to this report.