Torrential downpours have swollen the Mississippi River, which could reach about 13 feet above its flood stage in St. Louis. Flooding could affect about 18 million people in states living along the river, from Minnesota to Louisiana.
In Missouri, flooding is blamed for at least 13 deaths -- 12 of which the governor called "preventable" -- and is forcing mandatory evacuations.
In the city of West Alton, there is just one northbound lane and residents have been told to get out, reports CBS News correspondent Anna Werner.
"We emptied out our basement of anything important. We cleaned out the house of clothes," said one West Alton resident, Kathy Wunderlich.
As the Mississippi River threatens St. Louis County, it took teamwork to fill 20,000 sandbags. Officials pleaded for help and the community responded.
"Just like the movie, 'Field of Dreams' -- if you build it, they'll come," said one resident.
The Army Corps of Engineers is monitoring 19 vulnerable levees on the rising Mississippi River and its tributaries.
In the shadow of St. Louis' majestic Gateway Arch, during the city's wettest year, the Mighty Mississippi is expected to crest at over 43 feet, close to its second highest level ever.
"Water levels in some areas expected to exceed the historic crest during the Great Flood of 1993," Missouri Gov. Jay Nixon said Tuesday, when the river crested 22 feet above flood stage in the city of Hannibal. The Great Flood affected nine states, nearly 150 major rivers and tributaries, and killed 50 people.
It has been more than 20 years since such extensive flooding hit the St. Louis region and the National Guard has been activated statewide to help fight the flood. In the city of High Ridge, residents are fortifying their treatment plant to keep the flood out of the drinking water that is supplied to thousands, after flooding pushed untreated sewage from a plant into nearby rivers and streams.
In Union city, water crept up over porch steps as rescue boats skipped by. Cindy Nations claims her home isn't prone to flooding.
"They would not sell me flood insurance, so I've never been concerned about it," Nations said.
Another state hard-hit by the torrential downpours is Illinois. At O'Hare International Airport in Chicago - one of the busiest in the country -- more than 150 flights have been cancelled, and nearly 130 delayed Wednesday as airlines scramble to get back on track after days of weather delays.