ALAMEDA, Calif. -- An Alameda beach that closed after oil was found in the sand Tuesday will remain closed until at least Thursday because of an unrelated sewage spill Wednesday afternoon, a beach spokeswoman said.

About 75 gallons of sewage leaked into the waters off Crown Memorial State Beach around noon, prompting East Bay Regional Park District officials to keep the beach closed until the water is tested, according to spokeswoman Shelly Lewis.

The sewage came from a clogged pipe in a residential area near the beach, Lewis said.

The waters off the beach will be tested and if the bacteria level is below the state standard the beach can reopen Thursday, according to Lewis.

The beach initially closed after a group of windsurfers emerged from the water with some tar on their hands around 12:45 p.m. Tuesday and park district investigators subsequently found tar balls the size of quarters and dimes scattered along a half-mile stretch of the beach, Lewis said.

The source of the tar balls has not been determined, but investigators do not believe the tar balls are a product of the Nov. 7 Cosco Busan oil spill into the San Francisco Bay, according to Lewis.

Clean-up crews finished combing the beach to remove oil and the U.S. Coast Guard sent samples of the oil to a lab to find out what kind it is and where it came from, Lewis said.

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.