Per CNN, they've just opened the Morganza Spillway in Louisiana...

http://www.bloomberg.com/news/2011-05-14/mississippi-river-floodgate-to-open-today-inundating-louisiana-cajun-area.html

Louisiana’s Morganza floodway will be opened today at 3 p.m., local time, sending torrents of brown water from the Mississippi River into the Atchafalaya River basin, a move designed to spare Baton Rouge and New Orleans.

The corps expects to release 150,000 cubic feet per second from the Morganza, which is 310 river miles above New Orleans. The spillway, built in 1954 and not opened since 1973, can release 600,000 cubic feet of water per second at maximum capacity. It may send enough water to fill a football field 10 feet deep every second across the heart of what is known as Cajun country, eventually filling an area almost as large as Connecticut.

About 2,500 people and 2,000 structures are within the spillway and another 22,500 and 11,000 buildings are vulnerable when the waters rise, according to Louisiana Governor Bobby Jindal. Inside the threatened area are 2,264 wells that each day produce 19,278 barrels of crude oil, about 10 percent of Louisiana’s onshore total, and 252.6 million cubic feet of natural gas, according to the state.

The water flow “is putting tremendous stress on the entire system,” said Major General Michael Walsh, president of the Mississippi River Commission. “I directed the commander to open those bays today.”
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http://www.bloomberg.com/news/2011-05-14/mississippi-river-floodgate-to-open-today-inundating-louisiana-cajun-area.html

Louisiana’s Morganza floodway will be opened today at 3 p.m., local time, sending torrents of brown water from the Mississippi River into the Atchafalaya River basin, a move designed to spare Baton Rouge and New Orleans.

The corps expects to release 150,000 cubic feet per second from the Morganza, which is 310 river miles above New Orleans. The spillway, built in 1954 and not opened since 1973, can release 600,000 cubic feet of water per second at maximum capacity. It may send enough water to fill a football field 10 feet deep every second across the heart of what is known as Cajun country, eventually filling an area almost as large as Connecticut.

About 2,500 people and 2,000 structures are within the spillway and another 22,500 and 11,000 buildings are vulnerable when the waters rise, according to Louisiana Governor Bobby Jindal. Inside the threatened area are 2,264 wells that each day produce 19,278 barrels of crude oil, about 10 percent of Louisiana’s onshore total, and 252.6 million cubic feet of natural gas, according to the state.

The water flow “is putting tremendous stress on the entire system,” said Major General Michael Walsh, president of the Mississippi River Commission. “I directed the commander to open those bays today.”
</snip>

14 May 2011 Last updated at 20:05 GMT

Mississippi floods: Louisiana gates open to save cities

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.