In Pass Christian, a Mississippi coastal community wiped out by hurricanes Camille and Katrina, Mayor Chipper McDermott was optimistic Isaac would not deal a heavy blow.
"It's not too bad, but the whole coast is going to be a mess," he said early Wednesday.
McDermott stood on the porch of the $6 million municipal complex built after Katrina, with walls of 1-foot-thick concrete to withstand hurricane winds. As he looked out toward the Gulf of Mexico, pieces of a structure that had stood atop the city's fishing pier washed across the parking lot.
The state transportation department said Mississippi Highway 43 and Mississippi Highway 604, both in Hancock County, were not passable because of storm surge driven inland.
In largely abandoned Plaquemines Parish, Campbell said an 18-mile stretch along the thinly populated east bank was being overtopped by surge. The levee had not broken.
Campbell said officials believe some people may be trapped in their homes by water from the overtopped levee but were not sure how many might still be in the area. Strong wind was hampering efforts of rescuers to get into parts of the area.
She said officials expected the water to recede to the Gulf as wind direction changes with the storm's movement..
Hundreds of thousands of people were without power across the state's southern parishes, including more than 250,000 in New Orleans and its suburbs, power provider Entergy reported.
Tens of thousands of people had been told ahead of Isaac to leave low-lying areas of Mississippi and Louisiana, including 700 patients of Louisiana nursing homes. Mississippi shut down the state's 12 shorefront casinos.