Over the next few days, water spewing through a Mississippi River floodgate will crawl through the swamps of Louisiana's Cajun country, chasing people and animals to higher ground while leaving much of the land under nearly seven meters of brown sludge.
The floodgate was opened Saturday for the first time in nearly four decades in an attempt to divert water from Baton Rouge, New Orleans and the numerous oil refineries and chemical plants along the lower reaches of the Mississippi.
Shifting the water away from the cities eased the strain on levees and blunts the potential for catastrophic flooding in an area that is still recovering from Hurricane Katrina. The water will flow 30km south into the Atchafalaya Basin, and from there it will roll on to Morgan City, an oil-and-seafood hub and a community of 12,000.
The Morganza spillway is part of a system of locks and levees built after the great flood of 1927, which killed hundreds and left many more without homes. This is the second such spillway to be opened in Louisiana.
The Morganza, a 1,200-meter long structure built in 1954, was expecting to only open up about a quarter of its 125 gates. Its opening marked the first time three flood-control systems have been unlocked at the same time along the Mississippi River, a sign of just how historic the current flooding has been.
Earlier this month, the army intentionally blew holes into a levee in Missouri to employ a similar cities-first strategy, and it also opened a spillway northwest of New Orleans about a week ago.
Snowmelt and heavy rain swelled the Mississippi, and the river has peaked at levels not seen in 70 years.
About 25,000 people and 11,000 structures could be affected by the oncoming water, and some people living in the threatened stretch of countryside - an area known for fish camps and a drawling French dialect - have already fled.