The storm has flooded neighbourhoods in a rural part of the state and in neighbouring Mississippi, although New Orleans has escaped the worst. The waters have been rising fast, even as Isaac, downgraded from a hurricane on Wednesday night, meandered slowly northward on a path toward neighbouring Arkansas.
President Barack Obama has declared federal emergencies in Louisiana and Mississippi, freeing up federal aid for affected areas.
Along the shores of Lake Ponchartrain just north of New Orleans, officials sent scores of vehicles to help move about 3,000 people as rising waters lapped against houses. Floodwaters rose waist-high in some neighbourhoods, and authorities worked to rescue people stranded in their homes.
Isaac passed slightly to the west of New Orleans, where the city’s newly fortified levee system, helped by £8.8 billion in federal repairs, easily handled the assault. But low-lying areas outside the city, some reliant on levees maintained on a parish basis, were swamped.
“Hurricane Isaac has reinforced for us once again just how vulnerable these critical areas are,” Democratic US Sen Mary Landrieu said.