It will be a few days before the soupy brown water recedes and people forced out of flooded neighborhoods can return home.
And the damage may not be done. Officials were pumping water from a reservoir to ease the pressure behind an Isaac-stressed dam in Mississippi on the Louisiana border. In Arkansas, power lines were downed and trees knocked over as Isaac moved north into the state.
The earthen dam on Lake Tangipahoa could unleash a 17-foot flood crest downstream in Louisiana if it were to give way, which prompted evacuations in small towns and rural areas Thursday. Officials plan to punch a hole in the dam to release excess water in a controlled fashion but were waiting for daylight Friday to decide exactly where and when, said Donnie Hodges with the Pike County, Miss., Office of Civil Defense.
New Orleans, spared any major damage, lifted its curfew and returned to its usual liveliness, although it was dampened by heavy humidity.
"I have a battery-operated fan. This is the only thing keeping me going," said Rhyn Pate, a food services worker who sat under the eaves of a porch with other renters, making the best of the circumstances. "And a fly swatter to keep the bugs off me -- and the most important thing, insect repellent."
The heat was getting to Marguerite Boudreaux, 85, in Gretna, a suburb of New Orleans.
"I have a daughter who is an invalid and then my husband is 90 years old, so he's slowing down a lot," she said, red in the face as she stood in the doorway of her house, damp and musky from the lack of air conditioning.
Isaac dumped as much as 16 inches of rain in some areas, and about 500 people had to be rescued by boat or high-water vehicles.
At least four deaths were reported in Louisiana and Mississippi.
The latest two victims, a man and a woman, were discovered late Thursday in a home in the hard-hit town of Braithwaite, south of New Orleans. Authorities said deputies went to search for the couple after someone reported they had apparently not escaped the flooding. Their names were not immediately released.
On Grand Isle, a barrier island on the Gulf, the town pumped away water. Sections of the only road to town had washed out.
On a street turned river in Reserve, on the east bank of the Mississippi River, two young men ferried their neighbors to the highway in a johnboat, using boards as paddles.
Lucien Chopin, 29, was last to leave his house, waiting until his wife and three kids, ages 7, 5 and 1 were safely away.
He was finally joining them late Thursday, hoping they would find a shelter.
His van was underwater and water flowed waist-high in the house he'd rented for eight months.
"It's like, everything is down the drain. I lost everything. I've gotta start all over."
Chopin was upset that pumps meant to keep the area dry either failed or were shut off.
"We knew it was coming, but they didn't tell us we had to evacuate. We had no idea it was gonna be like this," he said, a refrain echoed by many.
Cisco Gonzales, a heating and air conditioning business owner, said he got his boat and truck and headed for higher ground when he heard the water was rising quickly, from 0 to 6 feet of water in five minutes.
"I've never seen so much water in my life," said Gonzales, who built a home in Braithwaite, southeast of the city, after his previous home was damaged by Katrina in 2005.
He rode out the storm at a ferry landing and when the weather calmed, he went out and rescued about a dozen people.
"I got back to my house to assess the situation, and it's a mess," he said. "That's all I can say."
Isaac hit on the seventh anniversary of Katrina, a hurricane that devastated New Orleans.
The two storms had little in common. Katrina came ashore as a Category 3 storm, while Isaac was a Category 1 at its peak. Katrina barreled into the state and quickly moved through. Isaac lingered across the landscape at less than 10 mph and wobbled constantly. Because of its sluggishness, Isaac dumped copious amounts of rain. Many people said more water inundated their homes during this storm than during Katrina.
Both storms, however, caused the Mississippi River to flow backward. And both prompted criticism of government officials.
In the case of Isaac, officials' calls for evacuations so long after the storm made landfall caused some consternation.
Jefferson Parish Council President Chris Roberts said forecasters at the National Hurricane Center in Miami needed a new way of measuring the danger that goes beyond wind speed.
"The risk that a public official has is, people say, `Aw, it's a Category 1 storm, and you guys are out there calling for mandatory evacuations,"' Roberts said.
Eric Blake, a specialist at the hurricane center, said that although Isaac's cone shifted west as it zigzagged toward the Gulf Coast, forecasters accurately predicted its path, intensity and rainfall. He did say the storm came ashore somewhat slower than anticipated.
Blake cautioned against using Katrina as a benchmark for flooding during other storms.
"Every hurricane is different," Blake said. "If you're trying to use the last hurricane to gauge your storm surge risk, it's very dangerous."
Crews intentionally breached a levee that was strained by Isaac's floodwaters in southeast Louisiana's Plaquemines Parish, which is outside the federal levee system. Aerial images showed the water gushing out.
In Louisiana alone, the storm cut power to 901,000 homes and businesses, or about 47 percent of the state. That was down to 39 percent, or about 821,000, by Thursday evening, the Public Service Commission said.
Entergy Corp., Louisiana's largest power company, said Isaac knocked out power to nearly 770,000 of its customers in Louisiana, Mississippi and Arkansas. Only three storms have left more customers without power: Hurricanes Katrina (1.1 million), Gustav (964,000) and Rita (800,000), the company said in a news release.
More than 15,000 utility workers began restoring power to customers in Louisiana and Mississippi, but officials said it would be at least two days before power was fully restored.
In Mississippi, several coastal communities struggled with all the extra water, including Pascagoula, where a large portion of the city flooded and water blocked downtown intersections.
High water also prevented more than 800 people from returning to their homes in Bay St. Louis, a small town that lost most of its business district to Katrina's storm surge.
Robbie Daniel, 55, an industrial engineer, and his wife, Kathi, a retired school teacher, live in a house on the Tchoutacabouffa River in Biloxi, and hadn't left home since Tuesday. Their house is on stilts and was surrounded by chest deep water.
Kathi saw online Thursday that casinos could be opening so they hopped in a kayak, paddled to their car on higher ground and drove to Island View Casino Resort in Gulfport.
"Tired of sitting there watching rain," Kathi said.