WINFIELD, Mo. -- Flood fighters tackled new slides and sandboils in a fragile earthen levee along the swollen Mississippi River on Wednesday, as forecasters said an overnight deluge of rain could cause a second round of big crests north of here.
As much as 8 inches of rain fell in parts of northern Missouri Tuesday and Wednesday, adding water to about four rivers there feeding into the Mississippi, the National Weather Service said.
"They will be dumping in huge, unwelcome amounts into the Mississippi over the next few days," hydrologist and meteorologist Mark Fuchs said. "It looks like it's mostly an issue from Hannibal to the south," he said. "Hannibal could go up to its big crests again."
That wasn't welcome news in Winfield, where flood fighters no sooner declared that their patch of Tuesday's 200-foot run of soil down the slope of the Pin Oak levee was holding when a 100-foot slide, a smaller shifting and sandboils emerged Wednesday.
Lincoln County authorities deemed the area extremely hazardous and ordered boaters out of the water, saying even slight wakes could prompt a catastrophic failure.
The porous and heavy soil of the Pin Oak is like a sponge, and the U.S. Army Corps of Engineers' chief of dam safety, Travis Tutka, has said he can't guarantee the levee would hold.
The two-and-a-half-mile-long levee about 45 miles northwest of St. Louis is all that's still protecting 100 houses, a city park, several businesses and 3,000 acres of agricultural land in east Winfield, one of the last towns where the upper Mississippi was expected to crest.
The latest forecast shows the Mississippi will crest at Winfield at 37.5 feet on Friday, more than 11 feet above flood stage.
Other towns were relatively dry despite the rain. Canton, about 25 miles from the Iowa border, took about 5 inches of rain overnight but the downpours didn't raise the river significantly. In Clarksville northwest of St. Louis, a weakened sandbag wall protecting the city's historic downtown was reinforced and was holding ahead of Friday's predicted crest of 36.9 feet.
U.S. Transportation Secretary Mary Peters promised $1 million in emergency relief for Iowa to help pay for urgent repairs to roads and bridges damaged by floods.
The disaster declaration for Missouri makes federal funding available to state and local governments and certain private not-for-profit groups to help deal with weather and water damage.
The declaration includes the city of St. Louis and counties of Andrew, Atchison, Buchanan, Cape Girardeau, Clark, Holt, Jefferson, Lewis, Lincoln, Marion, Mississippi, New Madrid, Nodaway, Pemiscot, Perry, Pike, Platte, Ralls, St. Charles, St. Louis, Ste. Genevieve and Scott.
Iowa officials said water quality tests show that floodwaters heading down the Mississippi River from Iowa contain large amounts of bacteria, sediment and fertilizers like phosphorus and nitrogen.
"When you have flooding of this scale, everything in the landscape is affected," said Iowa Department of Natural Resources spokesman Kevin Baskins.
So far, tests have not turned up large amounts of industrial chemicals or other volatile materials in the water, he said. Personnel in Iowa are locating and removing all the floating propane tanks or other floating canisters they can find.
Associated Press reporters Cheryl Wittenauer and Christopher Leonard in St. Louis and Sam Hananel in Washington contributed to this report.