Floodwaters from the bloated Mississippi River and its tributaries spilled across farm fields, cut off churches, washed over roads and forced people from their homes in the poverty-stricken Delta region.
People used boats to navigate flooded streets in the Delta as the crest rolled slowly downstream, bringing misery to poor, low-lying communities.
Hundreds have left their homes in the Delta in the past several days as the water rose towards some of the highest levels on record.
The flood crest is expected to push all the way through the Delta by late next week.
“It’s getting scary,” said Rita Harris, 43, who lives in a tiny wooden house in the shadow of the levee in the Delta town of Rena Lara, with a population of 500. “They won’t let you go up there to look at the water.”
Officials in the town, which has no local newspaper or TV stations, tried to reassure residents that they were doing what they could to shore up the levee would warn people if they needed to leave.
Mississippi governor Haley Barbour urged people to get out if they thought there was even a chance their homes would flood. He said there was no reason to believe a levee on the Yazoo River would fail, but if it did 107ft of water would flow over small towns.
“More than anything else, save your life and don’t put at risk other people who might have to come in and save your lives,” he said.
Last night US president Barack Obama signed a disaster declaration for 14 counties in Mississippi because of the flooding. Housing and home repairs will be covered and low-interest loans to cover uninsured damage will be available.
The Mississippi Delta, with a population of about 465,000, is a leaf-shaped expanse of rich soil between the Mississippi and Yazoo Rivers, extending about 200 miles from Memphis, Tennessee to Vicksburg, Mississippi.
While some farms in the cotton, rice and corn-growing Delta are prosperous, there is also grinding poverty. Nine of the 11 counties that touch the Mississippi River in Mississippi have poverty rates at least double the national average of 13.5%, according to the US Census Bureau.
The governor said the state was asking local authorities to get in touch with people who might have no electricity and phones and thus no way to get word of the flooding.
“It’s a tiny number, but we have to find them,” Mr Barbour said.
In Greenville, unemployed Liz Jones, who lives on the second floor of a housing project, worried what might happen in the event of a levee break. She said dhe had no means of transportation.
“I got a baby and my mama. I don’t know what we’d do about food and clothes and stuff,” she said.
Swollen by weeks of heavy rain and snowmelt, the Mississippi has been breaking high-water records that have stood since the 1920s and 30s. It is projected to crest at Vicksburg on May 19 and shatter the mark set there during the cataclysmic Great Flood of 1927. The crest is expected to reach New Orleans on May 23.
Even after the peak passes, water levels will remain high for weeks and it could take months for flooded homes to dry out.
About 600,000 acres of cultivated row crops could flood, mainly winter wheat, corn, soya beans, cotton and rice, said Andy Prosser of the Mississippi Department of Agriculture.
Even if the levees hold, the state expects to lose $150-$200m (€105-€140m) worth of crops, the governor said. Mississippi’s catfish farmers could also be wiped out if the Yazoo floods their ponds and washes away their fish.
Many of the victims of the slowly unfolding disaster are poor people living perilously close to the water.
In the Memphis, Tennessee area, where the Mississippi crested on Tuesday just inches short of the 1927 record, many of the flooded dwellings were mobile homes and one-storey brick or wood buildings in low-lying, working-class neighbourhoods unprotected by floodwalls or levees.