Tides predicted to peak shortly after Thanksgiving could wash sticky, thick balls of oil off beaches and spread them to places previously unaffected after a cargo ship hit a bridge this month, spilling 58,000 gallons of fuel.
Most of the oil floating on the water has already washed up on beaches or was recovered by cleanup teams by early last week, according to an environmental study of the spill, federal and state officials said Sunday.
More than 16,000 gallons of oil had been collected, and another 4,000 gallons had evaporated by Sunday, according to a statement issued by the Coast Guard and wildlife officials.
The agencies' environmental report said that tar balls could persist in the San Francisco Bay through the end of the month. As sand begins sticking to the globules of oil, they may begin to sink, the report said.
The freighter Cosco Busan struck the San Francisco-Oakland Bay Bridge in heavy fog on Nov. 7. Federal prosecutors are doing a criminal investigation of the spill. Officials are focusing on the actions of the ship's pilot and crew.
The lasting effects of the spill on Bay Area ecosystems was underscored Sunday when a dead bird covered in oil was recovered on a beach south of San Francisco that had been cleaned and reopened on Friday.
The number of oiled birds found dead or that died after being taken to rescue centers has neared 1,400, while the total number of birds blackened by the spill topped 2,000.
About 18 beaches and piers remained closed over the weekend while cleanup crews worked to recover more oil before the onset of higher tides.
The agencies' analysis said there was a "slight chance" that some oil could reach as far as Ano Nuevo, a pristine wilderness coastline more than 40 miles south that hosts the world's largest mainland breeding colony for the northern elephant seal.
"A few scattered tar balls" could also end up near the Farallon Islands, a wildlife refuge about 26 miles off the coast, if strong winds over the next week push the oil out to sea, the report said.
Background on the oil spill response effort is online at www.coscobusanincident.com