By midday Saturday, the storm had dumped up to 5 inches of rain in parts of Illinois. And the National Weather Service said it was bringing more rain and some drought relief to parts of the Mississippi and Ohio River Valleys.
In Louisiana, the number without power was down from more than 900,000. However, in heavily populated Jefferson Parish near New Orleans, parish president John Young said Entergy Corp. was too slow in restoring electricity.
"I don't see boots on the ground," said Young, who complained that he has seen repair trucks sitting idle in a staging area and fielded calls from residents and business owners complaining about a lack of progress.
"We've restored about 45 percent of our customers in about a day and a half, Entergy spokesman Chanel Lagarde said. He added that crews have come in from 24 states. "In many situations, crews have driven all day and have worked their 16-hour day and have to rest for the day."
New Orleans Mayor Mitch Landrieu said he too was anxious to get power back on. "Like everybody else, my patience is wearing thin," he said.
On Saturday afternoon, St. Tammany Parish officials ordered a mandatory evacuation of areas south of the Pearl River diversion canal, for fear a lock on a canal will fail. Parish authorities said the order could affect anywhere from several hundred to 2,000 residents in the rural area north of Slidell.
Parts of coastal Plaquemines Parish, where thousands were evacuated, remained under water. The National Weather Service has said Isaac dumped anywhere from 10 to 20 inches of rain on south Louisiana and south Mississippi.
In the water-logged town of Lafitte, Mayor Tim Kerner was allowing property owners and residents to return and begin cleaning up.
Meanwhile, Gulf of Mexico oil platforms were being repopulated after Isaac forced shutdown of most Gulf oil production.
People stuck inside stuffy, powerless homes were comparatively lucky. The governor's office said more than 4,000 were in state, local or Red Cross shelters as of Saturday morning and that doesn't count others who took refuge with friends, family or in hotels.
LaPlace resident Roshonda Girrad was staying in a state-run shelter in Alexandria, 200 miles from her home. She was waiting for the chest-deep waters in her neighborhood to recede.
"The showers are horrible. The food is horrible," Girrad said. "I'm not from around here. I don't know what's going on. We're in the dark."
Isaac dumped as much as 16 inches of rain in some spots, and about 500 people had to be rescued by boat or high-water vehicles.
In New Orleans, most of the downtown area and the French Quarter had power again Saturday. The annual Southern Decadence festival, a celebration of gay culture, was underway. And the Superdome, which sustained minor damage, prepared to host a Saturday night football game between Tulane and Rutgers.
Newly nominated Republican presidential candidate Mitt Romney visited flood-ravaged communities on Friday, and President Barack Obama said he would arrive Monday appearances this part of the country is all too familiar with after Hurricane Katrina in 2005 and the 2010 Gulf oil spill.
To the east, officials pumped and released water from a reservoir, easing the pressure behind an Isaac-stressed dam in Mississippi on the Louisiana border. The threat for the earthen dam on Lake Tangipahoa prompted evacuations in small towns and rural areas.
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. Parish President Billy Nungesser said the work was slow-going.