The swollen Mississippi River ran over the top of at least 12 more levees on Wednesday, as floodwaters swallowed up more U.S. farmland, adding to billion-dollar losses and feeding global food inflation fears.

Corn grows in a flooded field near Ladora, Iowa, Friday, June 13, 2008. Floods that have inundated the Midwest could reduce world corn supplies and drive food prices higher at a time when Americans are already stretching their grocery budgets and people in poor countries have rioted over rising food costs. (AP Photo/Sue Ogrocki)

Volunteers and aid workers were piling sandbags up and down the most important U.S. inland waterway to try to protect more levees and thousands of acres of prime crop land threatened as the river's crest moves south after last week's torrential rains.