Several Southern California beaches will remain closed over the weekend as officials investigate an oily substance that washed ashore over the last couple of days.

Nearly every beach on the Los Angeles South Bay , when the tar balls first began washing up, according to the Los Angeles Times. Cleanup crews were immediately dispatched to the area to collect the black globs.

"Investigators have said the tar has moderate hazardous characteristics and is slightly flammable," the report added. "The substance has tested positive for low amounts of volatile organic compounds."

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But the one conclusion investigators haven't drawn is where the tar balls came from. A recent oil spill in central California, but it will take several days , the Associated Press reported.

The Coast Guard also said there is a refinery and offshore oil tanker terminal near the area where the tar balls were found, but they couldn't find a sheen that would accompany a possible spill, the AP added.

The closure , NBC Los Angeles said. Six and a half miles of beach , the Coast Guard confirmed to CNN.

MORE ON WEATHER.COM: California Oil Spill

Spilled oil covers the beach at Refugio State Beach as the Channel Islands are seen in the distance on May 19, 2015 north of Goleta, Calif. (David McNew/Getty Images)