"It's not the largest spill we've ever had, but it's a large one," said Louisiana Department of Environmental Quality spokesman Rodney Mallett after visiting the scene. (See the extent of the spill in the accompanying video.)
The river remained closed between Mile Marker 98, near the Harvey Canal, and Mile Marker 40, downstream from New Orleans near Port Sulphur, and at least 26 vessels were backed up awaiting passage as of 5:00 p.m. CDT Wednesday.
The river could remain closed for days, and full cleanup could take weeks, a Coast Guard spokesman said.
"They hope it won't take that long," he said.
Three refineries with 560,000 barrels per day of capacity were in the affected area, although there were no reports of effects on refinery operations. Some are served by pipeline rather than by vessel traffic on the river.
The Coast Guard was investigating a report that the crew on the tugboat Mel Oliver, which was pushing the barge at the time of the accident, was unlicensed.
About 420,000 gallons of fuel, described as lighter than crude oil but heavier than diesel fuel, spilled from the barge. Nothing leaked from the Tintomara, which was carrying styrene and biofuels, officials said.
A Coast Guard spokesman said the fuel oil will dissipate faster than crude oil but more slowly than diesel fuel. A sheen spread down river, but Mallett said environmental impact was limited.
Air quality readings in the vicinity were not beyond limits, and no wildlife impacts were reported, he said.
Drinking water intake from the river was diverted or closed in the area and citizens were asked to conserve water use to maximize supplies pending resumption of water treatment operations, the New Orleans water department said.
Cleanup crews spread 45,000 feet (13,720 meters) of boom, or floating barriers, to try to contain the oil and keep it out of sensitive areas, and skimmers likely will be used to remove the spilled oil, a Coast Guard spokesman said.
A Coast Guard environmental strike team also was on scene, along with helicopters and a Coast Guard vessel, the Coast Guard said. The tanker was anchored at the scene.
Tugboats were holding pieces of the barge near the Crescent City Connection bridge, downstream from Harvey Canal, officials said.
Refineries in the area include Chalmette Refining, which handles up to 193,000 bpd, and ConocoPhillips' Belle Chasse refinery with 247,000 bpd capacity, both of which reported no impact.
Chalmette Refining is a joint venture between Exxon Mobil and Venezuelan state oil company, PDVSA.
Murphy Oil , which owns the 120,000 bpd refinery at Meraux, did not respond to telephone calls.