HOUSTON – The largest petroleum spill at New Orleans since 2005's Hurricane Katrina snarled Mississippi River traffic Thursday and brought flows of grain and other products to a virtual standstill, the Coast Guard said.

The day after a ship collision shut down a 97-mile stretch of the river from New Orleans to the Gulf of Mexico, 91 ships and barge tows were waiting to move along the vital link to Midwest grain elevators, coal terminals and other industrial facilities, a Coast Guard spokesman said.

Officials deployed an armada of ships to contain the spill, a floating scrim of 420,000 gallons of No. 6 fuel oil that threatened to contaminate the area's drinking water.

Coast Guard officials said they were hoping to reopen the river within a few days but the cleanup would take weeks.

“Traffic is stopped both inbound and outbound,” a Coast Guard spokesman said, counting 21 vessels northbound, 38 southbound and 32 on the Gulf Intracoastal Waterway, where it crosses the river, as of Thursday afternoon.

The spill happened early Wednesday when the tanker Tintomara, owned by Whitefin Shipping Co of Gibraltar, hit an American Commercial Lines barge being pushed by the tug Mel Oliver.

The 600-foot tanker, carrying styrene and biodiesel bound for Europe, split the 190-foot barge in half, dumping the fuel. The tanker was not seriously damaged, a spokesman said.

The Coast Guard continued to look into a report that the tugboat crew was not properly licensed, a spokesman said.

A spokesman for Minneapolis-based Cargill, the world's largest grain exporter, expressed hope the shutdown will be short.

At the Port of South Louisiana, largest in the area, barges could still arrive from the U.S. heartland but ships headed out to the Gulf of Mexico and foreign ports were “essentially frozen,” a person familiar with operations said.

“We just finished loading one that can't leave the river simply because there's no place to go,” the source said of a shipload of iron headed overseas.

The spill was the largest in the area since Hurricane Katrina in 2005 collapsed oil tanks at an area refinery, and Louisiana officials said it was the largest in the river since a tanker ran aground southeast of New Orleans in 2000.

A major coal shipping terminal south of New Orleans, United Bulk Terminal, which sends coal to other parts of the United States and overseas, declared force majeure on deliveries pending reopening of the river.

No wildlife impact had been reported yet, but the Louisiana Department of Environmental Quality was monitoring, spokesman Rodney Mallett said.

New Orleans' drinking water appeared to be safe, officials said. Arrangements were being made to accommodate suburbs whose freshwater intakes had to be closed temporarily.

The tanker and the floating halves of the barge were still being held near the site of the accident, but salvage operations on the vessels were expected to begin Thursday, the Coast Guard said.

Three refineries are located in the area of the spill along with two major coal-loading terminals, United and one operated by Kinder Morgan. There were no reports of impacts on the refineries.

The refineries are operated by ConocoPhillips, Murphy Oil and Chalmette Refining LLC, a joint venture between Exxon Mobil and Venezuelan state oil company PDVSA.

“We get most of our crude via pipeline, so that means that we can operate without issues for a couple of days,” said ConocoPhillips spokesman Bill Graham.

(Additional reporting by Janet McGurty in New York and K.T. Arasu in Chicago; Editing by Chris Baltimore and Christian Wiessner)