WINFIELD, Mo. — With a few days to go before the last stretch of the bloated Mississippi River reaches its crest, people toiled around the clock Monday to reinforce levees already strained and saturated from the pressure of the rising water.

Officials in Lincoln County asked for volunteers to help fill 50,000 sandbags to fortify the 2 1/2-mile-long Pin Oak levee, an earthen berm that was so waterlogged that it was like "walking on a waterbed," said county emergency management spokesman Andy Binder. Federal officials said they couldn't be sure it would survive through the river's crest at Winfield later in the week.

"They have a serious condition on their hands," Travis Tutka, the U.S. Army Corps of Engineers chief of dam safety, said late Monday afternoon. "This will be quite a test of that levee."

If it breaches, the river will swamp 100 homes in east Winfield, as well as 3,000 acres of farm fields, several businesses and a city ballpark. A muskrat burrowed a hole in the soft ground during the night, releasing a geyser of water, and officials said it took nearly six hours to choke off the leak.

"There is no guarantee of performance, but we're fighting the good fight," Tutka said.

Only a handful of residents remained in Winfield on Monday, after emergency workers went door to door urging them to evacuate. Among the holdouts was Sherman Jones, 56, who was all alone in his house except for his dogs, Mugsy and Junior.

"There is no place to go but the high school. I am not going to leave 'til my feet are wet," Jones said. "It's been a rough year, but we'll get through it."

Elsewhere in the hard-hit county a few dozen miles north of St. Louis, National Guard soldiers patrolled levees looking for soft spots.

Down river in Grafton, Ill., Mayor Richard Mosby said about 20 homes and businesses were flooded — but no more were expected to be affected if the Mississippi crests as forecast just a few inches above Monday's level.

The river's crest was not expected to reach Grafton and Winfield until Thursday or Friday, according to the federal river forecast issued Monday afternoon.

Upriver, where the river already had crested, officials nervously stood watch Monday as they waited for the danger to recede. Lt. Gen. Robert Van Antwerp, the Army Corps' chief of engineers, toured Clarksville on Monday afternoon and said he was most concerned about agricultural levees up and down the river.

"I think what they have is holding well," Van Antwerp said. "Now, it's a matter of getting the water off of it."