A group of windsurfers found tar balls on their hands after they emerged from the water on Tuesday afternoon, which prompted the initial closure because officials found more scattered along the beach.
On Wednesday afternoon, a clogged residential pipe caused about 75 gallons of sewage to pollute the same sands, district officials said.
Officials waited for water tests to show that bacteria levels at the beach cooperated with state regulations.
Just after 5 p.m. today, district Assistant General Manager Rosemary Cameron said the test results had come back and the water toxin levels were far below what state regulations allow.
The source of the oil never surfaced but investigators did not believe it came from the Cosco Busan spill in November 2007 because the tar balls were too fresh.
The oil was found near a bird sanctuary but no oiled birds have been reported. Reports of oiled birds or additional oil should be made at the Park District's Public Safety Department at (510) 881-1833.
Information regarding beach status is available by calling (510) 544-2208 or online at http://www.ebparks.org.