Patches of oil reportedly crept to within two miles of the Louisiana bayous and threaten to reach shore if wind and current change. But authorities said calm weather will help oil stay offshore in the next three days.

A 72-hour forecast shows winds shifting to the south and blowing about 12-17 miles per hour, which is likely to produce only "a little bit of movement on the fringes," said Charlie Henry with the National Oceanographic and Atmospheric Administration.

However, coastal areas likely to be affected are on alert for the first major landfall of the oil slick, as experts warned that the oil could kill wildlife and damage livelihoods for thousands of people living along in the coastal states.

Parish and state officials in Louisiana have enacted plans to keep the oil out of the marshes at the heart of the state's fishing industry and wildlife habitat.

"If it gets back into the backwaters, into the bayous, that's where we'll kill off the food chain," said Billy Nungesser, president of Plaquemines Parish.

"That's where it will devastate southern Louisiana for years to come, and we will lose our heritage in the fishing industry," he said.

Nungesser said his staff have divided up the parish into 13 separate zones for booms to be deployed, depending on the trajectory of the oil spill.

A large barge arrived from Port Fourchon Tuesday night and was deployed from Venice Wednesday afternoon to be a supply post for fishing boats and other crews to deploy soft, white absorbent booms when oil gets closer to shore.

"We're drawing our line in the sand and we're going to draw it right where the marsh begins," Nungesser said. "There is no cleanup in Plaquemines Parish. Prevention is the only way to do this and that's for all of coastal Louisiana," he said.

An explosion occurred April 20 at the Deepwater Horizon drilling rig, about 42 km southeast of Venice, Louisiana. Eleven workers were killed.

The rig, owned by Swiss-based Transocean and leased by BP, sank April 22 after burning for roughly 36 hours and the untapped wellhead continues gushing oil into the Gulf of Mexico.

About 1.6 million gallons of oil have spilled since the explosion, according to the Coast Guard. Experts warn of an environmental and economic catastrophe if oil continues to leak.