County health officials warned people on Aug. 8 to avoid the waters of Mother’s Beach in Marina Del Rey and the in Santa Monica Pier due to high levels of bacteria.   On July 28, the warning was first issued to several beaches in the area, including beaches in Santa Monica, Will Rogers State Beach and Catalina Island. Warnings were lifted for all beaches except Mother’s Beach and the Santa Monica Pier.   July 11 Sewage Spill  While the cause of the elevated bacteria levels is uncertain, the warning comes after nearly 17 million gallons of raw sewage from the Hyperion Water Reclamation Plant was dumped into Playa Del Rey beach on July 11.   The City of Los Angeles Sanitation & Environment (LASAN) said in a statement on Aug. 5 that debris caused backup in the plant, triggering a “controlled emergency measure” which resulted in the discharge of untreated sewage into …