The overflowing Mississippi River has already topped levees in northern Missouri after steady downpours last week in Iowa, Missouri and Illinois, the St. Louis Post-Dispatch reported Wednesday.
Now more rain is expected to speed up the melting of snow and raise or slow the fall of already flooding rivers in Illinois, Missouri, Iowa, Indiana, North Dakota, Mississippi and Michigan, the National Weather Service said.
The Post-Dispatch reported the Mississippi River should crest Wednesday and hover at 35.5 feet -- 5.5 feet over flood stage -- through Thursday before slowly receding in Missouri.
Volunteers, prison inmates and Missouri National Guard soldiers built an eight-foot-high wall of gravel and sandbags in Clarksville, Mo., Tuesday as the river crested there. The Mississippi rose to 35.3 feet in Clarksville on Monday and fell one-half foot Tuesday, the Post-Dispatch said.
"Now we wait, watch, hope and pray," said Kathy Weiss, Clarksville's emergency director. "We're pretty comfortable that it will hold."
Residents of Grafton, Ill., may see the worst of the rising Mississippi River waters, which could crest at more than 11 feet above the flood stage, the National Weather Service said.
Four people have died -- one in Illinois, one in Missouri and two in Indiana -- and thousands have been displaced due to the flooding, CNN reported.