Inmates move sandbags for the construction of temporary levees in Butte LaRose, Louisiana, May 14, 2011. [Photo/Agencies]

Protecting New Orleans

Failing to open the spillway would have put New Orleans at risk of flooding that, according to computer models, would eclipse that seen during Hurricane Katrina in 2005, when 80 percent of the city was flooded. About 1,500 people died in the disaster.

In addition to threatening densely populated areas, lower Mississippi flooding threatened as many as eight refineries and at least one nuclear power plant alongside the river.

The refineries make up about 12 percent of the nation's capacity for making gasoline and other fuels.

In the Atchafalaya River basin, authorities went door to door to begin evacuations in small towns and parishes in the path of the water, which could take weeks to reach the Gulf of Mexico.

Louisiana Governor Bobby Jindal said on Friday the state had plans with the American Red Cross to provide shelters for evacuees. "I'm very scared," said Heidi Fangue, a Morganza resident. "I have my bags packed and ready to go."