A barge laden with 80,000 gallons of oil struck a railroad bridge in Vicksburg, Miss., over the weekend, spilling light crude into the Mississippi River and closing the waterway for miles each way, the Coast Guard said. A second barge was damaged.

Although an oily sheen was reported up to three miles downriver from Vicksburg, investigators were uncertain how much of the oil had spilled when the bridge was hit early Sunday, Coast Guard spokesman Lt. Ryan Gomez said.

"Investigators are still trying to figure out what happened," he said by telephone from Coast Guard offices in Memphis, Tenn.