VICKSBURG, Miss. — Cleanup crews with booms skimmed oily water from the Mississippi River a day after a barge holding more than 1,900 barrels’ worth of oil struck a railroad bridge near Vicksburg, spreading a sheen of light crude that kept part of the waterway shut to ship traffic Monday, authorities said.

It remained unclear Monday morning how much oil had leaked into the river, according to the Coast Guard and U.S. Army Corps of Engineers.

Coast Guard spokesman Petty Officer 3rd Class Jonathan Lally said Monday afternoon that oil was “still discharging, but it is slowly discharging.”

He said crews were looking for oil roughly 50 miles downriver from the site.

“It’s minimal, if any, environmental impact due to the swift current” further downriver, Lally said.

He said the investigation is continuing closer to the site, but there was still no word on how much oil had leaked or how long it would take to transfer oil from the damaged barge to another barge.

The spill backed up at least 24 tugboats, barges and other vessels on the normally bustling corridor, said Kavanaugh Breazeale, spokesman for the U.S. Army Corps of Engineers in Vicksburg. The river was closed to traffic for 16 miles - eight miles north and eight miles south of Vicksburg.

Breazeale said it was uncertain how long the river would remain closed.

He said the damaged barge had eight tanks and each tank could hold about 1,904 barrels of oil. A barrel is 42 gallons. He said the investigation had shown that one tank was pierced above the water line.

“It’s not leaking that much oil,” Breazeale said.

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.

Twelve northbound vessels and 12 south bound vessels were waiting to pass Monday, according to Breazeale.

Herman Smith, superintendent of the Vicksburg Bridge Commission of Warren County, said the railroad bridge gets hit about once or twice a year, usually during floods. During the 2011 flood, it was hit five times in two weeks.

The river isn’t in flood stage now, Smith said. It was at 33.5 feet Sunday.

Coast Guard spokesman Lt. Ryan Gomez said investigators reported that a towboat or tug was pushing two tank barges when the crash occurred about 1:30 a.m. Sunday.

The second barge was damaged, Gomez said.

Authorities inspected and declared the railroad bridge safe for trains after the crash Sunday. That day, the oily sheen was reported up to three miles downriver from the bridge.

Gomez said crews had laid down a main boom and a secondary boom. They also were using a rotating skimmer device to sweep up oily water in the river.

“They have the boom to contain any crude oil that’s leaking out of the barge. They have a secondary boom to corral any crude oil that gets past the first boom,” Gomez said. United States Environmental Services, a response and-remediation company, was working on the booms and collecting the oily water, he said.

He said crews also were in the process of working to transfer the remaining oil.

“They are continuing to try to remove the product from the damaged tank to one of the nondamaged tanks on the same barge,” he added. “The ultimate goal is to transfer all of the crude to a different barge.”

The oil sheen was unlikely to pose a threat to the Gulf of Mexico, more than 340 river miles south of Vicksburg.

Gomez said the barge was southbound at the time of the collision, but investigators were still trying to figure out exactly what happened.

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.

Both vessels were being pushed by the tugboat Nature’s Way Endeavor. The website for Nature’s Way Marine LLC of Theodore, Ala., identifies the vessel as a 3,000-horse power, 90-foot long boat. It was built in 1974 and underwent a complete rebuild in 2011, according to the company.

A company manager referred calls to the Coast Guard command center at Vicksburg.

Information for this article was contributed by Janet McConnaughey and Lisa J. Adams of The Associated Press.

Front Section, Pages 4 on 01/29/2013