"My family is split up," said Angela Serpas, from severely flooded Braithwaite. Serpas and her daughter were staying with her in-laws while her husband and son were staying in Belle Chasse, a suburban area of the parish.
"This is the second time we've lost our home. We lost it in Katrina," she said.
At least seven people were killed in the storm in the U.S. - five in Louisiana and two in Mississippi.
President Barack Obama was to visit Louisiana Monday, a day ahead of the Democratic convention. Republican presidential nominee Mitt Romney visited the state Friday.
Progress was evident in many places. Workers continued their return to offshore oil and gas production platforms and drilling rigs, electricity came on for hundreds of thousands of people and the annual Southern Decadence Festival, a gay pride celebration, carried on in the French Quarter.
There were also signs of a slow recovery. Workers continued to deal with toppled trees and downed power lines, driving remained hazardous in areas without working traffic lights, and New Orleans opened two cooling shelters so those with no electricity could escape the heat.
Much of Plaquemines Parish, a vulnerable finger of land that juts into the Gulf of Mexico southeast of New Orleans, remained under as much as 5 feet of water, Parish President Billy Nungesser said. The Category 1 hurricane walloped the parish, and for many, the damage was worse than Katrina in 2005.
"I've never seen water come up this quick this fast," he said.
He said there were reports that cattle in the largely rural parish took refuge on porches. In one instance, cattle broke through a window and lumbered onto furniture to stay above water.
Suburban communities farther north also had problems. Near Lake Pontchartrain, St. Tammany Parish officials kept watch over potential trouble spots along Isaac-swollen waterways.
An evacuation near the community of Bush was dialed back Sunday after authorities stabilized a lock in danger of failing on the Pearl River Diversion Canal. St. Tammany spokeswoman Suzanne Parsons said officials shifted their focus to the West Pearl River and a flood threat to roughly 5,000 homes there.
In Mississippi, Gov. Phil Bryant reported 125,000 people were evacuated, though most returned home Sunday. Less than 100 people remained in shelters. Bryant said 924 people had to be rescued during Isaac.
Entergy, which provides power to most of the people who lost it, was under fire over the weekend from local government officials for what they said was a slow pace of restoration. Jefferson Parish President John Young said widespread outages were hampering businesses' recovery from the storm and he would ask the state Public Service Commission to investigate.
Entergy spokesman Chanel Lagarde noted that Isaac had lingered over the state after Tuesday's landfall and said Friday was the first day the corporation could get restoration efforts into high gear.
"We are working hard. We do have a good plan and we're going about it in an approach that we think is going to be effective," Lagarde said.
In Mississippi, about 1,600 Entergy customers awaited power. Roughly 5,000 served by not-for-profit electric associations also had no service.
Homeland Security Secretary Janet Napolitano met with Mississippi emergency officials and Bryant at a fire station in Bay St. Louis, Miss., and was scheduled to make a stop in Louisiana later in the day.
Bay St. Louis was devastated by Katrina seven years ago, but this time it was protected from Isaac's surge by a new seawall.
Burdeau reported from Bay St. Louis, Miss.