Water pours though a break in the Pin Oak levee Friday in Winfield, Mo. A new defense is in the works: a quickly constructed 4-foot-tall sandbag levee to protect 100 homes in the floodwater's path.

Winfield, Mo. ? A heroic effort by hundreds of townspeople, volunteers and National Guardsmen to hold back the Mississippi River failed Friday – undone by a burrowing muskrat.

The furry rodent dug a hole through the earthen levee in this eastern Missouri community, allowing water to penetrate the floodwall, which failed shortly before dawn.

“It’s so disappointing,” said Linda Wilmesherr as she peered through binoculars at water pouring through a gap that appeared to be 30 feet wide. “With all the guns in this county, couldn’t we kill a muskrat?”

But within hours, defiant residents were mounting a new defense – a quickly constructed 4-foot-tall sandbag levee to protect 100 homes in the floodwaters’ path.

“We’re not quitting – the Army doesn’t quit,” said National Guard Col. Michele Melton. “That’s why we’re here – to try and save these people.”

Many of the 720 residents of Winfield and people from nearby communities have spent the last several days helping the National Guard patch one trouble spot after another.

Wilmesherr operates a horseback riding school and suspended her business so she and her employees could bring in equipment and help save the levee.

In the end, their efforts were undone by an animal weighing no more than 5 pounds. Officials said the muskrat was either seeking food or building a den when it dug the hole that brought the levee down.

“How bad do I feel? You have no idea,” said Travis Tutka, the Army Corps of Engineers’ dam safety expert who helped coordinate the effort to save the levee. “The challenge we met for so long out here – I can’t come up with the words for the feeling. The levee did as well as it did because of the resolve of the people who worked on it.”

The only good news was the location of the breach – at the far southern corner of the levee. That meant floodwaters would have to cover 3,000 acres before approaching a cluster of homes at the north edge of the flood plain – a process that would probably take several hours.