As the thick, black sludge continues flowing toward the Gulf of Mexico, crews are up against the clock to stop it.

"Currently, we have deployed 500 people that's manning those booms and also doing shoreline cleanup," said Paul Book from American Commercial Line.

"We have placed that equipment in the sensitive areas, near water intakes,” he added. “We're monitoring the water intakes."

The company is using the booms to block off large sections of oil, but with the work zone now stretching more than 100 miles down the Mississippi River, it will take quite an effort.

More than 400,000 gallons of oil threaten the environment -- from wildlife to drinking water.

But Coast Guard officials say they are seeing some progress.

"We still have a lot, a huge amount of oil left out there moving down the river, but I was very encouraged to see the change in what's out there,” said Capt. Lincoln Stroh from the Coast Guard. “Areas where there was 90 to 80 percent coverage on my over flight yesterday are now 50 to 40 percent coverage."

Officials say they've recovered 225 barrels of oil.

But with thousands more still drifting, the Coast Guard can't say when the river will reopen for business.

"I do not want to give a date right now.  Like I said, we're still thinking in terms of days," Stroh said.

"We're prioritizing all the needs and the cargo that are currently in the queue out there. Right now we have about 60 vessels in the queue. So that's part of getting this marine transportation system back up and running, which is one of my top priorities."

While the cleanup remains the most pressing concern, an investigation is underway into the cause of the oil spill, which could cause losses in the millions of dollars for river business.

The tugboat hired to transport the oil barge remains the focal point, as officials say no one onboard was properly licensed to operate the boat.

Officials are "looking into both the ship and the tow, and all the incidents that led up to that -- including who was hired and who was working at the time -- so, really can't comment much more than that; it's all part of the investigation," Stroh said.