A swell of water is moving down the Mississippi River, threatening a catastrophe not seen since the Great Mississippi Flood of 1927.That event still ranks as one of the worst natural disasters in American history. In part, that flood catalyzed the mass migration of millions of African-Americans to northern cities, propelled Herbert Hoover to the presidency and set the stage for the Great Depression. For more on 1927 flood, see “Rising Tide: The Great Mississippi Flood of 1927 and How It Changed America.”

For many, this flood will be worse. Read about some of the similarities of this flood to the 1927 disaster.

And in a nightmare scenario, it could damage significant sectors of the U.S. economy, affecting investors everywhere in addition to those with homes and businesses in the South and Southeast. See slideshow of Mississippi River flooding.

Spurred by intense rainfall, the flood will be the biggest test of the modern levee system since its creation in the aftermath of 1927. See National Weather Service flood-prediction map.

The weakest link? The Old River Control Structure in Red River Landing, La.

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