Three million acres, an area almost the size of Connecticut, may go under water as the Mississippi River flooding moves south, Louisiana’s governor said Tuesday.

“Based on inundation maps we are looking at, about 3 million acres in Louisiana will be under water,” Gov. Bobby Jindal said at a news conference in Baton Rouge. About 2,500 people inside the floodway may be affected and 22,500 may be affected by backwater flooding, he said.

The river was expected to hold just below 48 feet for a day in Memphis before the floods move south toward Louisiana and then empty into the Gulf of Mexico past New Orleans in about two weeks.

To relieve the threat to New Orleans and Baton Rouge, Louisiana’s capital, the Army Corps of Engineers may open the Morganza floodway. Opening the floodway halfway would inundate a swath of central Louisiana along the Atchafalaya River with 5 feet to 20 feet of water. The decision to open the floodway may come as soon as Saturday, Jindal said.

“The trigger is 1.5 million cubic feet of water a second going past the Red River Landing,” Jindal said. “We are at approximately 1.36 million right now.”

The Red River Landing is 63 miles north of Baton Rouge, near where the Louisiana state line moves east from the river. The Morganza floodway is between the landing and Baton Rouge.

The Mississippi, the largest river system in the country and the third-largest watershed in the world, drains 41 percent of the continental U.S., according to the Corps.

“If the Morganza is not opened and the levees are breached, the downstream destruction would be worse,” Fred Bryan, a professor emeritus of renewable natural resources at Louisiana State University in Baton Rouge, said in a telephone interview. “Once the river, with that cutting capacity and speed, cuts a hole you better get after it because it’s going to erode away the cut very quickly.”

The rising water has interrupted coal shipments to power plants in Tennessee, flooded more than 100,000 acres of Missouri cropland, forced thousands from their homes and prompted the Corps to open the Bonnet Carre Spillway to reduce the river’s force through New Orleans.

On the Mississippi between New Orleans and Baton Rouge, there are 11 refineries with a combined capacity of 2.5 million barrels a day, or 13 percent of U.S. output, according to Andy Lipow, president of Lipow Oil Associates in Houston.