MANHATTAN BEACH, Calif. >> Popular beaches along nearly 7 miles of Los Angeles-area coastline were off-limits to surfing and swimming Thursday as scientists looked for the source of globs of tar that washed ashore.

The sand and surf on south Santa Monica Bay appeared virtually free of oil after an overnight cleanup, but officials weren’t sure if more tar would show up. They planned to assess during low tide at midday.

U.S. Coast Guard and state officials said samples of tar and water would be analyzed to identify where it originated, but it could take days to get the results. Nothing has been ruled out, including last week’s coastal oil spill that created a 10-square-mile slick about 100 miles to the northwest off the Santa Barbara County coast.

There is also a refinery and offshore oil tanker terminal nearby, but the Coast Guard did not find a sheen from a spill after the tar started to accumulate Wednesday.

No problems with wildlife have been reported, said Sau Garcia of the California Department of Fish and Wildlife.

Lifeguards chased a handful of surfers out of the water, but beach life was otherwise normal for people exercising, playing volleyball, skating and riding bikes along the shore.

"I got a couple waves in and then they came by again and told me to get out," said Scott Berk, who regularly surfs at Manhattan Beach.

He said surfers are used to seeing bits of tar in the water and on the shore from natural seafloor seepage, but the amount that came in Wednesday was concerning.

"I hope they clean it up quickly," he said.

Public health officials told people to avoid contact with the water, wet sand or any material that washed up in the area. They warned that contact with petroleum products can cause skin irritation and result in long-term health problems.

Officials said it appeared to be about a barrel or two of oil — nothing like the Santa Barbara spill that killed some 16 birds and nine marine mammals, including dolphins and sea lions.

A small amount of tar also was reported Wednesday about 60 miles to the north in Oxnard, officials said.

Jane Hamburg, 54, of Cincinnati, saw news of the tar on TV and came down expecting black beaches. Instead, she found clean, groomed sand and no shortage of joggers, bicyclists and dog walkers.

"Looks good from where I’m standing," she said in Manhattan Beach. "I was expecting it to interrupt my day. Now, I just hope the sun comes out."