Officials in Louisiana plan to take the rare step of opening a massive spillway to divert some of the Mississippi River, swollen by months of flooding.

The U.S. Army Corps of Engineers said it will begin opening the Morganza Spillway gates one at a time Sunday.

The spillway diverts millions of gallons of water into farmland and campsites in the Atchafalaya Basin instead of allowing the massive flood to head downstream toward Baton Rouge and then New Orleans.

Officials tell The Advocate they expect to release less water this year than the last time the spillway was opened in 2011. But they stress with more rain falling north in the Mississippi River basin, their calculations could change.

The spillway was built in 1954 and has been opened just twice before.