Investigators did not know how much had spilled, but an oily sheen was reported as far as three miles downriver of Vicksburg after the 1:12 a.m. accident, said Lt. Ryan Gomez of the Coast Guard's office in Memphis, Tenn.
It wasn't immediately clear whether the second barge also hit the bridge or if it ran into the first barge, he said. The first barge was still leaking Sunday evening, and emergency workers set out booms to absorb and contain the oil, Gomez said. The river's closure halted at least five northbound and two southbound vessels, he said.
The bridge was found safe for trains, said Petty Officer Carlos Vega.
Both barges 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-horsepower, 90-foot-long boat, making it the largest and highest-powered of the company's five tugs. 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.
The Coast Guard Marine Safety Unit Vicksburg sent a team to assess the spill and oversee the cleanup, a Coast Guard news release said. The agency said a command center at Vicksburg included representatives from the Coast Guard and Nature's Way, as well as local officials and law enforcement.
The lower Mississippi River last closed because of an oil spill for less than a day last February, after an oil barge and a construction barge collided, spilling less than 10,000 gallons of oil. The oil barge was hit above the water line. In 2008, a fuel barge collided with a tanker and broke in half, dumping 283,000 gallons of heavy crude into the waterway, and closing the river for six days.
The oil sheen from Sunday's incident was unlikely to pose a threat to the Gulf of Mexico, located 344 river miles south of Vicksburg.
Residents and businesses in Gulf Coast states are still recovering from the April 2010 explosion of the Deepwater Horizon drilling rig, which killed 11 workers and spewed more than 200 million gallons of oil into the Gulf.