Robert Sanders rows his boat through floodwaters in front of his home with his dog Lucky in Holly Grove, Arkansas May 10, 2011.[Photo/Agencies]

MEMPHIS/NEW ORLEANS - The swollen Mississippi River set a record high water level at Natchez, Mississippi, on Wednesday -- 10 days before its expected crest in the southern city.

The level of the largest river in North America reached 58.48 feet at Natchez on Wednesday afternoon, according to the National Weather Service, above the record of 58.04 feet set in 1937. The river is expected to crest at 64 feet on May 21.

The flood, the result of a wet spring and huge snow melt from an unusually stormy winter, has caused evacuations of thousands of people along the river and its tributaries, swamping river towns and as many as 3 million acres of farmland in Mississippi, Tennessee and Arkansas alone.

In Mississippi, residents were bracing for expected record crests at Vicksburg on May 19 and Natchez on May 21. Up to 5,000 Mississippi residents may be forced to evacuate, authorities said on Wednesday.

Thunderstorms are also expected on Thursday night into Friday, which could bring another inch of rain into the area.

Natchez, about 135 miles north of New Orleans, was bracing for higher water in coming days. But so far, levees along the river were holding, the US Army Corps of Engineers said.

"We're continuing to watch and wait and monitor the situation," said Jim Pogue, a Corps spokesman. "Everything is performing as we had hoped."

Meanwhile, the Corps said it may open the Morganza Spillway in Louisiana this weekend to ease the flooding threat to New Orleans and Baton Rouge. In a worst case scenario, if the Spillway is not opened, water levels in New Orleans could go as high as 25 feet, the Corps said.

The volume of water passing at Red River Landing north of Baton Rouge, Louisiana, will trigger any order to open the Spillway. The volume must reach 1.5 million cubic feet per second, a level the Corps expects to be reached on Saturday.

"The bottom line is we need to hope for the best and plan for the worst," said Louisiana Gov. Bobby Jindal. "The best thing we can do is be overprepared."

Jindal said 3 million acres of farm and wetlands in Louisiana were at risk of flooding.

In Mississippi, 16 casinos remain closed along the river and two more in Vicksburg were being monitored, said Allen Godfrey, deputy director of the Mississippi Gaming Commission.

The closures have put 13,000 employees temporarily out of work and will hurt local and state government tax revenues, which draw $19.7 million a month from casino boats.

Plans were under way to protect livestock and pet animals from the rising waters. A 300-animal shelter in Natchez began accepting evacuees' pets on Wednesday, while the Vicksburg City Shelter moved out all its animals and closed in anticipation of flooding, according to state emergency officials.

Tourism Draw?

But Vicksburg and Natchez city officials said most tourist attractions remain open and won't be affected. Connie Taunton, the Natchez tourism director, even touted views of the historic flood as a tourism draw.

"We sit high up on a 200-foot bluff," said Taunton. "We are high and dry. If people want to come to Natchez and see a historic event... there is no better place to see it."

The 2011 flood has been breaking or challenging records set during historic floods in 1927 and 1937.

The Bonnet Carre spillway near New Orleans was opened on Monday for the first time since 2008. Last week, the Corps blew up a section of the Birds Point levee in Missouri, submerging about 130,000 acres of farmland to ease the flood threat to Kentucky and Illinois river towns.

If Morganza is opened, it would be the first time three of the river's floodways were opened.

Since the Mississippi River flood of 1927 that killed some 1,000 people, improvements have been made in flood control with the building of dams and levees, reservoirs and floodways.

The river at Memphis, Tennessee, crested about a foot below the local record on Tuesday. Bob Nations, Shelby County Emergency Management director in Tennessee, said high water and a "hazardous environment" are going to be facts of life in Memphis for some time.

"This baby is not as ugly as it could have been, but it's still ours to raise," Nations said.