Waging war against flooding of historic proportions that has already affected thousands of people in eight Midwestern and Southern states, the U.S. Army Corps of Engineers opened a spillway Monday north of New Orleans in an effort to calm the rising Mississippi River.

A crowd gathered near the entrance to the Bonnet Carre spillway to watch workers using cranes slide open the gates to the flood control system, which was built beginning in 1929 after a devastating flood two years before. The spillway, like another that could be opened next week, is designed to divert floodwater away from New Orleans and slow the raging river to protect the low-lying city.

While the river's highest levels may still be days away, a decision to open the second flood control structure -- the Morganza Spillway -- may not be, Gov. Bobby Jindal said. People with property that would flood if the spillway is opened should not dally, Jindal warned.

"My advice to our people is not to wait, to get prepared now," Jindal said. - [ time mag flood pics ]

Upstream in Memphis, Tennessee, residents and authorities had prepared all they could Monday as they anxiously waited for the Mississippi to crest Tuesday morning at a near-record 14 feet above flood stage.

"It's sort of torturous, we've been waiting so long. It's hard keeping peoples' attention. It's warning fatigue, if you will," Memphis Mayor A.C. Wharton Jr. said. "But we're ready for it."

Water levels on the Mississippi

The river is the highest it's been at Memphis since 1937, when it crested at 48.7 feet -- 14.7 feet above flood stage. That flood killed 500 people and inundated 20 million acres of land, said Col. Vernie Reichling, the Corps' Memphis District commander.

The river Monday covered the lowest parts of the city's historic Beale Street and had forced about 400 people from their homes, Wharton said. Another 1,300 remained in low-lying areas, he said.

While Corps' officials said it appeared levees protecting the area were holding up well, with only minor amounts of water seeping in from beneath or lapping over from above, local officials were taking no chances.

"It's a very powerful river. It looks like it's running very slowly, but it has a very strong current," said Bob Nations, director of preparedness in Shelby County, Tennessee, which includes Memphis. "We still don't know (exactly what) the river might do."

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Nicholas Pegues, an East Memphis resident who lives near the Wolf River, said he's seen extensive flooding and homes left uninhabitable by the water as he's traveled through the region.

"It's affecting daily life tremendously," said Pegues, a Shelby County elections' division employee who submitted photos of the flooding to CNN iReport. "It is pretty severe downtown. ... I know a lot of ... people have lost their homes."

iReport: Flooding in downtown Memphis

The flooding also hit sections of southwest Memphis, along the Nonconnah Creek.

"It's just bad," James Black told CNN affiliate WREG-TV in Memphis. "Like I say, it's an act of God. What can you do in an act of God?"

Wharton, the city's mayor, said the flooding had not yet caused major disruptions in the city, and he did not expect it to, even though National Weather Service meteorologist Bill Borghoff said it is possible the river won't fall below flood stage at Memphis until June.

Memphis businesses prepare for flooding

That's the problem in Missouri and southern Illinois, where flooding continues even though the Mississippi and Ohio river crests have moved south.

In Murphysboro, Illinois, CNN iReporter Robert Icenogle said a swollen creek is inundating a church and band shell, while threatening to wash out telephone poles.

"We cannot get to the park, which is underwater, or to other towns," he said. "Most of the roads are closed, plus the water sewage plant is getting sandbagged."

"(If) the sewage plant shuts down, we won't have tap water to bathe in or drink," he added.