Louisiana Gov. Bobby Jindal says coastal officials may intentionally break a levee on the east bank of Plaquemines Parish to relieve pressure on the structure.
At a news conference in Baton Rouge, Jindal said there's no estimate on when that might occur. He says as many as 40 people are reportedly in need of rescue in the area.
He says Plaquemines Parish has ordered a mandatory evacuation for the west bank below Belle Chasse. That affects about 3,000 people in the area -- and a nursing home with 112 residents.
A shelter opened at noon in Belle Chasse.
Officials said the evacuation was ordered out of concern that more storm surge from Isaac would be pushed into the area and levees might be overtopped.
