The lower Mississippi River was partly shut to ship traffic as cleanup crews skimmed oily water Monday, a day after a barge with more than 80,000 gallons of oil struck a railroad bridge near Vicksburg, Miss., spreading a sheen of light crude.
Coast Guard and Army Corps of Engineers officials said they didn't know how much oil leaked.
The spill backed up at least 24 tugboats, barges and other vessels on the normally bustling corridor, said Kavanaugh Breazeale, a spokesman for the Corps of Engineers. The river was closed to traffic for 16 miles -- eight miles north and eight miles south of Vicksburg.
Breazeale said the damaged barge had eight tanks and each tank could hold 80,000 gallons of oil. He said the investigation had shown that one tank was pierced above the water line.
"It's not leaking that much oil," Breazeale said, though the exact amount was not known.
He also said it was uncertain how long the river would remain closed.
Coast Guard spokesman Jonathan Lally said crews are working on skimming oil that is contained in a boom.
Tugs were holding the barge near shore on the Louisiana side of the river, south of the bridge it hit and directly across from Vicksburg's Riverwalk Casino.
Orange containment boom was stretched across part of the river downstream from the barge, and a small boat appeared to patrol the area.
Coast Guard spokesman Lt. Ryan Gomez said investigators reported that a towboat or tug was pushing two tank barges when the accident occurred about 1:30 a.m. Sunday.
The second barge was damaged, Gomez said, and authorities inspected and cleared the railroad bridge afterward.
He said investigators are trying to figure out what happened.
The oil sheen was unlikely to pose a threat to the Gulf of Mexico, located more than 340 river miles south of Vicksburg.
The barges are owned by Third Coast Towing LLC, Gomez said. According to a website listed under that name, the company is located in Corpus Christi, Texas. A woman who answered the phone Monday at Third Coast Towing LLC declined to comment.