"It's minimal, if any, environmental impact due to the swift current" downriver, Lally said.
He said the investigation is continuing closer to the site, but there is still no word on how much oil has leaked or how long it will 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 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.
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 southbound vessels were waiting to pass Monday, according to Breazeale.
Coast Guard spokesman Lt. Ryan Gomez said investigators reported that a towboat or tug was pushing two tank barges when the collision 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 collision Sunday. That day, the oily sheen was reported up to three miles downriver from the bridge.