|Residents of small Louisiana towns brace for a surge of water that could inundate thousands of homes [Reuters]
Authorities all over Louisiana's Cajun country have warned residents to head for higher ground to avoid water gushing from the Mississippi River, after a floodgate was opened for the first time in four decades.
Most heeded the warning, hopeful that the flooding engineered to protect the heavily populated cities of New Orleans and Baton Rouge would be merciful to their way of life.
People in towns where the floodwaters are expected spent days filling sandbags to try to protect their homes and clearing out their belongings.
By Sunday, some areas were virtually empty as the water from the Mississippi River, swollen by snowmelt and heavy rains, slowly rolled across the Atchafalaya River basin.
John Terrett, Al Jazeera's correspondent in Butte Larose in Louisiana, said authorities did the best they could to manage a difficult situation.
"In many senses, this is extraordinary situation - we are talking about the forced flooding of thousands of kilometres of farmlands and homes and business to the west of Baton Rouge and New Orleans in order to preserve those cities," he said.
"People have no choice but to sandbag their homes and get out - that is the extraordinary nature of this disaster. It was not a comfortable decision [made by authorities in charge] but the people here are very unhappy, they feel let down.
"The reason they did it is the economy of New Orleans. It is responsible for something like 13 per cent of all US oil production...and that port is the busiest port in terms of tonnage in the western hemisphere - to close it for even one day would cost $300m."
About 25,000 people and 11,000 structures could be affected by the oncoming water. The floodwaters could reach depths of 20 feet in the coming weeks, though levels were nowhere close to that yet.
The spillway's opening diverted water from heavily populated New Orleans and Baton Rouge - along with chemical plants and oil refineries along the Mississippi's lower reaches - easing pressure on the levees there in the hope of avoiding potentially catastrophic floods.
The Morganza spillway is part of a system of locks and levees that was built after massive flooding in 1927, which killed hundreds and left many more homeless. It took about 15 minutes to open the 8.5m gate on Saturday.
The opening of the Morganza marked the first time that three Mississippi flood-control systems have been used simultaneously.
Water will flow 32km south into the Atchafalaya basin, and from there into Morgan City, community of 12,000 people. Eventually, the waters will flow into the Gulf of Mexico.
The spillway could remain open for weeks, depending on river flow levels.