Mississippi residents raced to shore up faltering levees Wednesday in hopes of holding back raging floodwaters that soaked cities upstream and are bearing down on one of the most poverty-stricken regions of the country.

In the town of Greenville, about 100 miles northwest of Jackson, officials were busy trying to patch up “sand boils,” spots where the Mississippi River was undermining the levee defenses.

Linda Wright was among a crowd of people who gathered near the river’s edge to get a glimpse of the rising waters that threaten their homes and farm fields.

“It’s just amazing the river has come up this far,” she said. “It just shows you there’s no limit to what nature can do. We just have to trust God.”

NPR’s Debbie Elliot, reporting from Mississippi, said “everyone’s worst fear” is that the pressure from the flood surge will cause the tributaries to start flowing backward — something that hasn’t happened since the Great Flood of 1927. If that happened, low-lying areas would be swamped and levees potentially breached.

“Right now, city officials think the levees will protect cities like Greenville, will protect Natchez and Vicksburg,” Elliott said.

In Vicksburg, the site of a pivotal Civil War battle, William Jefferson paddled slowly down his street in a small boat, past his house and around his church, both flooded from the bulging river.

“Half my life is still in there,” he told The Associated Press, pointing to the small white house swamped by several feet of water. “I hate to see it when I go back in.”

Jefferson has refused to leave his neighborhood, one of the hardest hit in the region. Instead, he guards what’s left of his possessions, waiting for the water to recede: “This is what I do every day. Just watch the water.”

But other people, familiar with stories passed down of the ‘27 flood, opted for a pre-emptive attack against the raging waters.

Elliot said tractor-driving farmers were frantically “plowing up wheat fields, plowing up fields that would be close to harvest right now, using that dirt to build earthen dams around homes, around the silos where the grain is, trying to protect the corn fields.”

Over the past week or so in the Mississippi Delta, the rain-swollen river and its backed-up tributaries have washed away crops, forced scores of people to seek higher ground and closed some of the dockside casinos that are vital to the state’s economy.

All 19 of Mississippi’s casinos along the river will be shut down by the end of the week, costing governments $12 million to $13 million in taxes per month, authorities said. That will put some 13,000 employees temporarily out of work.

But the worst is yet to come, with the crest expected over the next few days.

The Mississippi crested in Memphis, Tenn., on Tuesday just inches from the record of 48.7 feet set during flooding in 1937, an event that looms nearly as large in the region’s psyche as the Great Flood of 1927. The damage in Memphis was estimated at more than $320 million as the most serious flooding began, and an official tally won’t be available until the river returns to the confines of its banks.

Brenda Terry was one of about 500 people forced to stay in Memphis shelters run by the Red Cross and other organizations. She told NPR that she couldn’t even get near her flooded-out mobile home because the roads leading to it were under water.

“There was stuff that I lost that I wouldn’t take nothing for. Pictures of my mom, pictures of my kids when they were in school,” Terry said. “I have to start from scratch.”

At some homes, polluted floodwaters reached up to the first-floor ceiling, while others were submerged. Snakes slithered in the foul water, and officials warned of bacteria. President Obama declared Memphis’ Shelby County and surrounding counties disaster areas, making them eligible for federal aid.

In Arkansas, which produces about half of the nation’s rice, more than 1,500 square miles of farmland have been swamped over the past few weeks, and the economic impact will be more than $500 million, according to the state’s Farm Bureau.

There were no early figures on the devastation in Mississippi. But with hundreds of homes already damaged, “we’re going to have a lot more when the water gets to where it’s never been before,” said Greg Flynn, a spokesman for the Mississippi emergency management agency.

Across the region, federal officials anxiously checked and reinforced the levees, some of which could be put to their sternest test ever.

About 10 miles north of Vicksburg, contractors lined one side of what is known as a backwater levee with big sheets of plastic to keep it from eroding if waters rise over the top as feared — something that hasn’t happened since the levee was built in the 1970s.

In Vicksburg, which is at the southern tip of the rich alluvial soil in the central part of the state, the river was projected to peak Saturday just above the record of 56.2 feet set in 1927. Farther south in Natchez, forecasters said the 1937 record could be shattered by 4 feet on Saturday.

Jimmy Mitchell, 46, said he and his wife and two children have been living in a loaned camper for more than week at a civic arena in the city of Tunica.

“There’s no sewage hookup. You go in a barn to take a shower,” said Mitchell, who is from the small community of Cutoff.

It’s a town that “lives from paycheck to paycheck” but it’s also a community where everybody sticks together, Mitchell said.

Widespread flooding was expected along Mississippi’s Yazoo River, a tributary that is backed up because of the bloated Big Muddy. The town of Rolling Fork, birthplace of the late bluesman Muddy Waters, was also in danger of being inundated.

In Louisiana’s St. Martin parish, prison inmates were filling sandbags to protect property that could be flooded should authorities open the Morganza Spillway to take pressure off levees protecting Baton Rouge and New Orleans.

Gov. Bobby Jindal said he was consulting with the Army Corps of Engineers and that “based on their inundation maps, you’re looking at 3 million acres in Louisiana that will be impacted, that will be under water.”

About 2,500 people and 2,000 structures would be affected if the spillway were opened, officials said.

With reporting from NPR’s Debbie Elliot in Mississippi and David Schaper in Memphis, Tenn. Material from The Associated Press was used in this story. Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.