New Orleans is sinking, and some scientists are predicting that the city could be underwater within a century.
Today more than two-thirds of the city is already about 8 feet (2.4 m) below sea level.
This sinking, or subsidence, is happening because the city of New Orleans was built on the soft silt of the Mississippi Delta.
To make matters worse, the surrounding marshlands and low-lying barrier islands that have protected the city from hurricane damage in the past are also sinking.
And if predictions about global warming and rising sea levels come to pass, the loss of land to the sea will take place even sooner.
Each year 25 square miles (65 sq km) of land in New Orleans are lost to the water.
Geologists are looking at possible solutions.
One is to build a 25-foot (7.6-m)-high wall across the southern part of the city.