NEW ORLEANS, Louisiana (CNN) -- The oil spill that closed the Mississippi River at New Orleans is costing the U.S. economy $275 million a day, the head of that city's port authority told CNN.
Tugboats hold up parts of a barge that collided with a tanker. The collision spilled 419,000 gallons of oil.
The cleanup has to be faster, said Gary LaGrange, so the hundreds of waiting ships can get to port to load and unload goods.
"Somebody's gotta move a little quicker," he said as workers spent hours doing labor intensive work to decontaminate each vessel in the area.
The spill initially covered about 90 percent of the surface of the river after a barge collided with a tanker Wednesday. Watch the lineup of ships in the river »
By Friday the oil covered 20 percent to 30 percent of the surface, said Coast Guard Capt. Lincoln Stroh.
The currents and river bends helped to isolate the oil against the banks, where it is more easily cleaned, he said.
"We have a lot less oil downriver. ... We're happy to see that," Stroh said.
Stroh said four vessels were being allowed to move on the river channel Friday based on the importance of their cargo. At least two vessels were going to and from the Exxon oil refinery in Chalmette, assisted by tugboats, the Coast Guard said.
"We're moving those that have the highest, most critical need to the port -- in this case a tank ship with crude oil to provide feedstock for one of the refineries," Stroh said at a midday news conference.
"We're getting the important cargo to the important places."
A Marine Transportation System Recovery Unit, whose members include industry representatives such as shipping agents, was helping to prioritize the ships.
The timetable for moving more ships will be determined by how long it takes to clean the vessels at a decontamination station, Stroh said. A second station was being set up at Venice, Louisiana.
The barge owned by American Commercial Lines Inc. that leaked the oil after the collision was being assessed to determine how much oil still is inside, he said, adding, "I don't think there's a lot."
Stroh said the goal is to start draining the remaining oil to prevent any more from flowing downstream.
The barge won't be lifted out of the water until sometime next week. The vessel is beneath one of the bridges that carries U.S. 90 over the Mississippi.
The spill of thick, smelly oil occurred just north of the massive bridges connecting downtown New Orleans to communities across the river. The oil slick quickly spread out along 98 miles of one of the nation's busiest waterways toward the Gulf of Mexico, and officials banned traffic from that stretch of river. About 9,900 barrels, or about 416,000 gallons, leaked.
The Coast Guard said more than 100 ships were stalled. Watch scenes from the oil spill »
Paul Book, vice president of operations for American Commercial, said five emergency spill contractors -- about 500 people -- were participating in the cleanup. They have laid out 104,000 feet of containment boom and collected 11,000 gallons of oil-water mixtures.
Stroh said oil skimmed from the surface of the water can be recycled. Shorelines are cleared using mops resembling large pom-poms, and areas are steam-cleaned if necessary.
Stroh said the oil, widely used as marine fuel, is heavier than diesel but lighter than crude.
The tug Mel Oliver, which had been hired to push the barge upriver, had no properly licensed crew on board, Coast Guard officials said Thursday. The tugboat pilot had only an apprentice mate's license instead of the required master's license.
The oil was being hauled from John W. Stone Oil Distributor in Gretna, said Coast Guard Petty Officer Jaclyn Young.
Two investigations are under way -- one by the Coast Guard and the other by the National Transportation Safety Board. See a map of where the spill happened »
Tom MacKenzie of the U.S. Fish and Wildlife Service said there have been few reports so far of oil-covered wildlife, but much of the shoreline hasn't yet been searched.
Plaquemines Parish shut off its water intake valves after the spill, and was banned from using the ferry to New Orleans, except for emergencies. Parish President Billy Nungesser said he is prepared to truck water in if necessary.
"We're running low on the east bank of Plaquemines. We thought we'd run out today," he said Thursday. He said the parish was still testing the level of contamination.
"We will not turn on the outtakes until we are 100 percent sure it is safe to drink," he said. "The whole Mississippi has a sheen on it."
The east bank has 1,500 residents, a coal depot, an oil storage facility and other commercial businesses, he said.
The west bank of Plaquemines Parish, population 22,000, was using water from Jefferson Parish, which has supply valves north of the spill, Nungesser said.
In southern Plaquemines, Boothville-Venice has ponds that can provide a 20-day water supply, he added.
The spill is much smaller than the ones that followed Hurricane Katrina in 2005, when the Coast Guard estimated that more than 7 million gallons of oil were dumped into the Mississippi and nearby waterways.