14 May 2011 Last updated at 16:05 ET
US army engineers have opened floodgates in Louisiana that will inundate up to three million acres of land in a bid to protect large cities along the Mississippi River.
The Morganza Spillway opened at 1500 local time (2000 GMT) to ease pressure on Baton Rouge and New Orleans.
This is the first time in four decades the level of the Mississippi has forced the floodgate to be opened.
About 25,000 people and 11,000 buildings could be adversely affected.
Read more from the original source:
Key Mississippi floodgates opened