The backwater levee was being "armored" by a heavy plastic coating to prevent it from washing out, he said.

CNN: Jindal: Morganza Spillway could open as early as Saturday

In addition to the mainline levee along the river, starting near Vicksburg and extending northeast for more than 20 miles, a so-called backwater levee offers shelter.

CNN: Jindal: Morganza Spillway could open as early as Saturday

The backwater levee is designed to keep water from backing into the Yazoo River delta and is designed lower than the mainline levee so that water can flow over it.

CNN: Jindal: Morganza Spillway could open as early as Saturday