A state official says an 18-mile levee in southeast Louisiana's Plaquemines Parish will be breached to relieve pressure on it created by floodwaters from Tropical Storm Isaac.

The official says the levee won't be breached Wednesday because of weather conditions but it will happen as soon as equipment can be brought to the site.

The parish is a sparsely populated area south of New Orleans that's outside the federal levee system. It's been hit by severe flooding because Isaac has been moving at only about 5 mph.

Louisiana Gov. Bobby Jindal says about 40 people have been rescued in the parish. Some had to be moved to safety by boat.

Forecasters say Isaac, which was downgraded Wednesday, is expected to produce more inland flooding overnight. Its fierce winds have left hundreds of thousands without power.