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 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 released extra water through the dam and were considering punching a hole in it to lower the rain-swollen reservoir.
Louisiana Gov. Bobby Jindal said Friday that the Tangipahoa River crested Thursday night and was expected to go down by 2 feet Saturday. He said Mississippi's work to alleviate pressure on the dam appeared to be working.
"So far, operations seem to be proceeding as expected, and they seem to be working," Jindal said.
Republican presidential nominee Mitt Romney was headed to Louisiana to tour the damage. Romney scheduled a last-minute visit Friday to Lafitte, La., with Jindal. Lafitte was the site of rescue efforts when Isaac's tidal surge pushed in through the night Wednesday and into Thursday.
Shortly after Romney said he would visit Louisiana, White House spokesman Jay Carney announced that President Barack Obama would visit the state Monday to examine water and wind damage from Isaac.
In the Republican stronghold of Jefferson Parish, Romney could expect a friendly reception. One Republican, Mike Townsend, 47, said he was curious what Romney will say about Isaac and approaches to protecting the area.
"I like his business sense," Townsend said.
In Lafitte, Richard Riley, 45, was pleased that Obama was coming to Louisiana.
"He needs to see the devastation and allocate the money that's needed to build new levees or do whatever is needed to protect us," Riley said.
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.
Drivers patrolled streets looking for gas and faced long waits at stations that had power Friday. Some stations were out of gas, but at others clerks said they had gas but no power to pump it.
At the Magnolia Discount Gas Station in New Orleans' Carrollton neighborhood, employee Gadeaon Fentessa said up to 50 drivers an hour were pulling in, hopeful they could pump. He had the gas, but no power.
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.
The remainder of the storm was still a powerful system packing rain and the threat of flash flooding as it headed across Arkansas into Missouri and then up the Ohio River valley over the weekend, the National Weather Service said.
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."
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.
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.
Gov. Jindal said Friday that state officials expected to have 70 percent of the water on the east bank of Plaquemines Parish out of the flooded region by mid-afternoon.
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.
Allen Barrilleaux, 28, spent Friday morning draining water from the engine of his flooded truck not far from a river in Mississippi's Hancock County.
He was going to ride out the storm with his wife, a friend, and 5-week-old son in their house, which is on stilts, but called for help Wednesday when the water crept close to the house and large pine trees from a nearby mill swirled in the water. They were evacuated by boat.
"He slept the whole damn way," Barrilleaux said of his infant son, Mason.
Water never got into the home and it never lost power.
"We could have rode it out easy but it's better safe than sorry," he said.
Watching for ant beds as he walked around his green Chevy, Barrilleaux said hurricanes are part of life here, but disasters can hit anywhere, whether it's tornadoes in the Midwest or a volcano in Hawaii.
"Life's cruel," Barrilleaux said, gripping a wrench with a greasy hand. Then he smiled.
"We're like that big old ant hill and a guy with a lawnmower just keeps mowing us down."
Contributing to this report were Associated Press writers Brian Schwaner and Stacey Plaisance in Crown Point, La.; Melinda Deslatte in Baton Rouge, La.; Kevin McGill in Houma, La.; Vicki Smith in LaPlace, La.; Holbrook Mohr in Waveland and Pass Christian, Miss.; and Jeff Amy in Pascagoula and Bay St. Louis, Miss.