VICKSBURG, Miss. — The Coast Guard said Tuesday that about 7,000 gallons of crude oil were unaccounted for aboard a leaking barge that had rammed a railroad bridge near Vicksburg on the Mississippi River, which remained closed for a third day as crews slowly pumped out oil.
Petty Officer Third Class Jonathan Lally said it is not clear that all of the 7,000 gallons leaked into the river. Some of it, he said, could have seeped into spaces inside the barge.
Lally said a plan to pump oil from the stricken barge onto another barge — a process known as lightering — had been approved but it was unclear how long that would take or when the river might reopen to vessels. He said the other barge was en route.
Environmental impact, Lally said, has been minimal because a boom is containing the leak around the barge and the leak is slow.
The economic impact is another matter.
At least 54 vessels, including towboats and barges, were idled Tuesday on the closed 16-mile stretch of one of the nation’s vital commerce routes.
Vessel traffic tends to be less in January than during peak harvest season, when grain from the US heartland is shipped south to be loaded onto ships near New Orleans.
‘‘The Coast Guard advised our hazardous materials unit that the river would be closed indefinitely to all traffic,’’ Lieutenant Julie Lewis of the Louisiana State Police said.