Quarter-sized tar balls and an oil sheen were found along a half-mile stretch of Crown State Memorial Beach Park in Alameda on Tuesday, forcing closure of the park and shoreline and prompting a multi-agency investigation into the cause.

Beachgoers began reporting the tar balls and oil sheen about 12:45 p.m. Crews from at least three agencies responded, and they immediately posted notices closing the park, officials said.

Many people speculated the tar balls and oil sheen were remnants from the Cosco Busan, the container ship that dumped 58,000 gallons of crude oil into the Bay in November after crashing into the Bay Bridge.

But neither the Coast Guard nor the state Department of Fish and Game could say for sure Tuesday if the oil found in Alameda was from the Cosco Busan spill.

Samples of the oil were taken from the beach and will be analyzed to determine its origin, officials from both agencies said. Results of those tests are expected within 24 to 48 hours, said Petty Officer Kevin Neff.

"We don't know what it is," said Shelly Lewis, public information officer for the East Bay Regional Park District. Oil has also washed up elsewhere in the East Bay, she said.

The Cosco Busan's fuel tank ruptured Nov. 7 when its pilot, John Cota of Petaluma, guided the ship into an anchorage of the Bay Bridge. The oil appeared on shores throughout the Bay Area and was linked to the deaths of more than 10,000 birds.

Cota was eventually charged in the accident and has had his pilot's license revoked. He could face 18 months in prison and more than $115,000 in fines.

The Coast Guard requested $10,000 from the National Oil Spill Response Fund to help in the clean up.