A levee near Winfield, Mo., that was holding back the flood waters of the Mississippi River broke early Friday morning, said the U.S. Army Corps of Engineers.
The levee broke at its south end at 6:20 a.m. New York time, despite sandbagging to increase its height.
Officials said the levee, which protects about 3,000 acres (1,215 hectares) of agricultural land along with a few dozen homes, had been reinforced over the past week.
It was the 36th levee to be overtopped in the past 10 days or so along the Mississippi as the river swelled after torrential rains further north.
"The levee simply sustained water levels higher than it was designed for and for a much longer period of time than anyone had hoped," the Corps said in a statement.
"Water had already risen above the top of the levee as it was built and was on sandbags that were added to its top. The continuing saturation of the soil was the likely cause of this breakdown," it said, saying it had no further details.
The Midwest storms and torrential rains have killed 24 persons since late May. More than 38,000 people have been displaced from their homes, mostly in Iowa where 83 of 99 counties have been declared disaster areas.
The National Weather Service forecast strong thunderstorms will continue through the day and into the night in central and southern Iowa and northern Missouri, with numerous flash flood watches, hail and high wind warnings.
Fears that as much as 5 million acres (2 mln hectares) of corn and soybeans have been lost due to the flooding pushed corn and livestock prices to record highs.
Chicago Board of Trade corn prices set a new record in overnight screen trading on Friday at $8.25 per bushel in the July 2009 contract, more than double the 40-year average for corn prices.
Corn is the main feedstuff for meat animals, main feedstock for producing ethanol fuel, and is used in hundreds of other food and industrial products throughout the economy.
Before the floods hit, stockpiles of corn in the United States, the world's largest exporter with a 54 percent market share, had already been projected to fall to 13-year lows next year.
Livestock prices have also set records and prices of soybeans are also hovering at record highs on supply worries.
"The crop had been improving but the big rains this week in southern Iowa and in Missouri stopped that trend, they probably deteriorated this week," said Jason Roose, a grain market analyst for U.S. Commodities in Des Moines, Iowa.
Roose, also a corn and soybean farmer, said, "Use me for example if you like. I planned to plant and replant soybeans around here this week but it didn't happen. I'm not able to do anything and everyone else around here is in the same boat."
Roose concluded, "The weather is just not good. An inch of rain is one thing, but these downpours are disastrous."