BUTTE LaROSE, La. — Cajun country residents threatened by Mississippi River flooding were packing their things this morning as they anxiously awaited word on when federal engineers could open a massive spillway that would inundate hundreds of thousands of rural acres and swamp thousands of homes.

The Army Corps of Engineers is close to opening the key Morganza floodway to relieve pressure on the levees downstream that protect the more densely populated Baton Rouge and New Orleans areas. The Corps could make the move as early as this weekend, though officials stress that no final decision has been made.

Still, the governor has warned residents in the spillway’s path to assume they’ll have to leave their homes. With that threat looming, some 25,000 people in an area known for small farms, fish camps, crawfish and a drawling French dialect are hurriedly packing and worrying that their homes and way of life might soon be drowned.

At a meeting Thursday, Army Corps of Engineers Col. Ed Fleming warned a crowd at a volunteer fire station that where they were standing was projected to be swamped by up to 15 feet of water from Mississippi River flooding. The crowd let out a collective gasp.

“From the ground?” an incredulous resident shouted.

“From the ground,” replied Fleming, head of the Corps’ New Orleans district.

Opening the gates for the first time in 38 years will unleash the Mississippi on a wild ride south to the Gulf of Mexico through the Atchafalaya River and divert floodwater from the river into the basin’s swamplands, backwater lakes and bayous. Several thousand homes would be at risk of flooding.

Even if engineers decide not to open the spillway, no one seems to doubt that a major flood is bound for Butte LaRose, Krotz Springs, the oil-and-seafood hub of Morgan City and other swampland communities in the Atchafalaya Basin.

The Morganza and the nearby Old River Control Structure were built in the 1950s to keep the Mississippi on its current course through New Orleans, one of the world’s busiest ports. If the river rises much higher at New Orleans, the Coast Guard said Thursday it would consider restrictions on shipping, including potentially closing the channel to the largest, heaviest ships.

Shipping interests have pushed for the opening of the Morganza, saying the move would keep ships cruising. If the river closes, history shows the costs grow quickly into staggering figures.

In 2008, a 100-mile stretch of the river was closed for six days after a tugboat pushing a barge collided with a tanker ship, spilling about 500,000 gallons of fuel and stacking up ships.