New Orleans' flood defenses appeared to withstand Hurricane Isaac, but thousands of people to the north and south of the city had to be evacuated or rescued as the storm lingered over the US Gulf Coast with whistling winds and constant rain.
The storm flooded neighborhoods in a rural part of the state and in neighboring Mississippi. The waters were rising fast, even as Isaac meandered slowly northward on Thursday on a path toward neighboring Arkansas.
US President Barack Obama declared federal emergencies in Louisiana and Mississippi, according to a statement from the White House, 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 evacuate about 3,000 people as rising waters lapped against houses.
Floodwaters rose waist-high in some neighborhoods, and authorities worked to rescue people stranded in their homes.
The floodwaters "were shockingly fast-rising, from what I understand from talking to people," Lt Gov Jay Dardenne said.
"It caught everybody by surprise."
Isaac arrived exactly seven years after the devastating Hurricane Katrina and passed slightly to the west of New Orleans, where the city's newly fortified levee system, helped by $14 billion in federal repairs, easily handled the assault. But low-lying areas outside the city were swamped.
"Hurricane Isaac has reinforced for us once again just how vulnerable these critical areas are," Democratic US Senator Mary Landrieu said.
One person was reported killed, compared with 1,800 deaths from Katrina in Louisiana and Mississippi. And police reported few problems with looting. New Orleans Mayor Mitch Landrieu ordered a dusk-to-dawn curfew.
But in Plaquemines Parish, a sparsely populated area south of the city that is outside the improved federal levee system, dozens of people were stranded in flooded coastal areas and had to be rescued.
The storm pushed water over an (29-kilometre) levee and put so much pressure on it that authorities planned to intentionally puncture the floodwall to relieve the strain. Officials rushed to evacuate more than 100 nursing home residents. In this mostly rural parish, even the sick and elderly are hardened storm veterans.
"I don't think we had to evacuate to begin with," said Romaine Dahl, 59, as he sat in a wheelchair.
"The weather was a hell of a lot worse last night than it is now."