Mike Stone, left, and Andy Sherman in the pumping station for Hannibal, Mo., during a flood in 1993. The city is protected by a flood wall, and flood managers have built up levees to protect against flooding. But scientists warn those structures are making flooding worse.
Two cars are submerged in floodwaters in a park in Kimmswick, Mo. Gov. Jay Nixon has declared a state of emergency because of widespread flooding around the state, which has closed many roads.
A steamboat drifts along the Mississippi River in New Orleans. A group called America's Watershed Initiative says "funding for infrastructure maintenance means that multiple failures may be imminent" for the lower Mississippi River basin.
Mario Tama/Getty Images
In the past decade, freshwater and sediment diverted from the nearby Mississippi River have turned what once was an open bay into a thriving wetlands area. Local environmental groups have planted thousands of cypress trees, attempting to create a marsh that will help absorb storms that pass through.
Weenta Girmay for WWNO
This is a calculated flood map for the city of St. Louis. Water depth goes from deep (dark blue) to shallow (white, light blue). Floodwater can come from the Illinois, Upper Mississippi and Missouri rivers, as well as from heavy local precipitation.
Courtesy of Dag Lohmann/Katrisk
The ill-fated Sultana in Helena, Ark., just before it exploded on April 27, 1865, with about 2,500 people aboard. Most were Union soldiers, newly released from Confederate prison camps.
Library of Congress
Workers pump water from the parking lot of the Dadeland Plaza shopping center on Thursday after heavy rains triggered by Tropical Storm Karen in Pinecrest, Fla., a suburb of Miami.
This WWII-era minesweeper once was a floating museum in St. Louis. Swept away in a 1993 flood, it has been under water in the river for most of the years since. But the ship has been exposed as the river's water level has fallen. (Photo taken on Dec. 14.)
Army Corps of Engineers