The National Weather Service is warning of a "dangerous and life-threatening situation" along the Arkansas River, which is expected to rise another three feet in the next few days.
The river has already overtaken roads and devastated communities like Fort Smith, where homes and businesses are surrounded by water. The river is expected to crest Wednesday around 20 feet above flood stage, breaking a record set in 1945 and causing potentially catastrophic flooding.
Near Barling, Arkansas, Sunday, two Army Corps engineers assessing a dam had to be rescued by helicopter after they were trapped by the rising waters. Floodwaters are putting stress on dams and levees.
Barling police officer James Breeden told CBS News' Manny Bojorquez that he's never seen the water so high and worries about the levees holding up.
"There is a concern about the integrity of the levees. They have never been tested to this limit before," Breeden said. "The potential impact is literally tens of thousands of people would be without a place to live. It would wipe out that many homes."
Even after the river crests, Breeden says it might not start to recede until Friday. It could be weeks before the water returns to its normal level.