If it weren't for the work of U.S. Army Corps of Engineers, the Mississippi River would not flow past New Orleans.

Recently, the main channel of the Mississippi was attempting to change its course and flow down the Atchafalaya River. This would have left Baton Rouge and New Orleans, both important ports without a navigable connection to the Gulf of Mexico. To prevent this, the Old River Control Structure (ORCS) was built in 1963 to let only 30% of Mississippi River volume into the Atchafalaya basin. Such controls have enormous impacts on the coastal wetlands of Louisiana.

More about coastal Louisiana.