SAN FRANCISCO (KGO) -- The United States Coast Guard and the California Department of Fish and Wildlife are investigating a reported fuel spill that occurred Saturday in the San Francisco Bay near Pier 45 at Fisherman's Wharf.
Coast Guard personnel in San Francisco received a report at 10:56 a.m. that an undetermined amount of fuel oil was discharged from the SS Jeremiah O'Brien, a World War II ship.
Crews were deployed Saturday to evaluate the spill and recover the discharged fuel.
Officials said it appears the spill occurred during an internal transfer onboard the vessel.
Crews are making progress containing the oil spill in the harbor home to the city's commercial fishing fleet.
An oil sheen about 150 yards long is lingering on the water inside San Francisco's Hyde Street Fishing Harbor and there's a full scale mission to stop it from spreading. At least 8,000 feet of boom is surrounding the harbor.
The environmental firm cleaning up the mess says it won't be easy. "It's a very dense black oil, a small amount of it can spread pretty far," NRC Environmental spokesperson Rich Betta said.
It's called bunker oil, a heavy grade crude, which was found leaking from the SS Jeremiah O'Brien, a World War II ship docked at Pier 45. The U.S. Coast Guard isn't sure how much got into the bay after a shipboard oil tank overflowed.
"What was reported to the coast guard was anywhere from five to fifty gallons so, we're still determining the quantity. We have coast guard inspectors on board doing sounding of the ships tanks and working with the crew to identify how much was discharged overboard," U.S. Coast Guard Lt. Jacob Aulner said.
The U.S. Coast Guard believes impacts to fish and wildlife will be minimal, but signs are going up at nearby Aquatic Park where swimming is now off limits.
Swimmer Christopher Jernberg and his friends decided to risk and swim anyways.
ABC 7 News spoke with Jernberg who said he didn't see any oil in the water.
The U.S. Coast Guard is now in charge of this large cleaning operation. It may take another two to three days to finish. Right now, it is unclear who will be getting the bill for the cleanup.
The cause of the spill is under investigation.
Bay City News contributed to this story.