Read local coverage at CNN affiliate WBRZ.
Angola, Louisiana (CNN) -- Prisoners in southeastern Louisiana are helping to fill sandbags and patch up levee holes along the swollen Mississippi in an all-hands-on-deck effort to keep the mighty river at bay.
At the Louisiana State Penitentiary, also known as Angola, parts of the sprawling prison complex are already underwater. An outer-ring levee was breached and some 2,000 inmates have been evacuated.
But an estimated 2,500 inmates are still at the prison, working to fill holes and keep the grounds dry. The 18,000-acre facility has a secondary levee that is currently holding the bulk of the water back.
The prison is bordered on three sides by the Mississippi River.
"This is 18,000 acres -- this is as large as Manhattan," said Burl Cain, the warden at Angola. "Think about evacuating Manhattan -- boom!"
Elsewhere in Louisiana, inmates in Pointe Coupee Parish have filled more than 110,000 sandbags, some of which were expected to be sent to St. Landry Parish, said CNN affiliate WBRZ. Others were used to shore up levees.
"The inmates take a lot of pride in doing this. They've been working very hard," said Point Coupee Sheriff Bud Torres, the station reported.
Like many states, Louisiana is struggling to cope with the worst flood to hit the lower Mississippi River valley since at least 1937.
Severe storms swept across the Midwest Sunday, bringing with them the threat of even more rain.
Louisiana Gov. Bobby Jindal has asked for federal assistance in grappling with flooding stemming from the Morganza Spillway, where 17 bays have been opened in hopes of sparing New Orleans farther downstream.
So far, the Louisiana Department of Transportation and Development has delivered nearly 150,000 sandbags, 30,000 cubic yards of sand and 33,000 linear feet of fabric-lined baskets, the governor's office said. Approximately 1,150 Louisiana National Guard members have been mobilized.
Mandatory evacuations were in effect Saturday in Happy Town and the Sherburne Wildlife Management Area, the St. Martin Parish Sheriff's Office said. Evacuations in Butte La Rose have been ordered to start on Tuesday.
Spillway gates are likely to be open for weeks, meaning it will be some time before the river falls below flood stage, allowing evacuees to return.
In just the St. Landry and St. Martin parishes alone, more than 3,000 people have evacuated, the governor's office said last week.
But so far, the prisoners left at Angola are holding their ground.
"There's a lot of worse places you can be," said inmate Darren Jarvis in response to a question about how he felt about working to save the institution that imprisons him. "I would hate to see what it would be like if I had to go somewhere else."