MANHATTAN BEACH, Calif. (KABC) -- South Bay beaches reopened Friday night, days after efforts to clean up an oily substance that washed ashore began.The beaches were reopened at about 6 p.m.The U.S. Coast Guard said the tar balls and patties that washed up on the beach Wednesday, amounting to more than three garbage truckloads, have been removed from El Segundo to Redondo Beach.The source of the oily substance is still unknown.U.S. Coast Guard Capt. Charlene Downey said testing will be done to determine the source, but that could take a week or more.The oil patties were spotted around noon Wednesday, closing the coastline in Manhattan Beach, Hermosa Beach and Redondo Beach.The beaches were temporarily closed from the lifeguard towers to the water, but visitors were able to use the area behind the lifeguard towers. Warning signs were posted urging the public to stay out of the water.Shoreline assessment teams were monitoring the area from Redondo Beach to Point Dume. Clean-up crews were also on standby in case more tar washed ashore.Those who spot more balls of tar are asked to call the National Response Center Hotline at (800) 424-8802.