NEW ORLEANS >> Isaac dropped unrelenting rain today, flooding areas north and south of New Orleans, and officials had to scramble to evacuate and rescue people as waters quickly rose. Inside the city, the fortified defenses held and life began to slowly get back to some sort of normalcy.

Along the shores of Lake Ponchartrain near New Orleans, officials sent scores of buses and dozens of high-water vehicles to help evacuate about 3,000 people as rising waters lapped against houses and left cars stranded. Floodwaters rose waist-high in some neighborhoods, and the Louisiana National Guard was working with sheriff’s deputies to rescue people stranded in their homes.

To the east, evacuations were ordered in a sparsely-populated area as a lake dam threatened to break near the Mississippi-Louisiana border. Officials in Tangipahoa Parish, La., feared the water it would pour into the already swollen river would flood low-lying areas downstream. Louisiana Gov. Bobby Jindal said officials there would release water at the dam.

Even as Isaac weakened on its slow trek inland, it continued to spin off life-threatening weather including storm surges, inland flooding from torrential rain and potential tornadoes. Nearly half of Louisiana electrical customers lost power and another 150,000 were out in neighboring Mississippi.

A Coast Guard helicopter hoisted a couple and their dogs this morning from a home in LaPlace, between the Mississippi River and Lake Ponchartrain, after storm surge poured into their neighborhood and local authorities called for help. The couple was taken to New Orleans and reported in good condition.

“The husband and wife and their two dogs were in an area where a lot of houses washed away,” said Lt. Cmdr. Jorge Porto. “They used a flashlight inside the house as a signaling device, which made all the difference in locating them effectively.”

The floodwaters “were shockingly fast-rising, from what I understand from talking to people,” Lt. Gov. Jay Dardenne said. “It caught everybody by surprise.”

A tow truck driver was killed this morning when a tree fell on his truck in Picayune, Miss., just across the state line from Louisiana. Authorities said Isaac was causing heavy rain and strong winds at the time.

President Barack Obama declared federal emergencies in Louisiana and Mississippi late Wednesday, allowing federal aid to be freed up for affected areas.

Isaac arrived seven years after Hurricane Katrina and passed slightly to the west of New Orleans, where the city’s fortified levee system easily handled the assault.

Louisiana’s Public Service Commission said 901,000 homes and businesses around the state — about 47 percent of all customers — were without power Thursday. Utility company Entergy said that included about 157,000 in New Orleans.

New Orleans’ biggest problems seemed to be downed power lines, scattered tree limbs and minor flooding. 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.

“Hopefully, as far as the city of New Orleans is concerned, the worst is behind us,” Landrieu said.

But in Plaquemines Parish, a sparsely populated area south of the city that is outside the federal levee system, dozens of people were stranded in flooded coastal areas and had to be rescued. The storm pushed water over an 18-mile 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 from Plaquemines Parish, an area with a reputation for residents hunkering down to weather storms and perhaps the hardest hit by Isaac. In this hardscrabble, 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. And I got an idea that after all this is said and done they’re going to say everything is over with, go on back home.”

Other residents in the Riverbend Nursing and Rehabilitation Center were loaded into ambulances and taken to a nearby naval station. Residents had their names and birth dates attached to their shirts.

By midafternoon Wednesday, Isaac had been downgraded to a tropical storm. The Louisiana National Guard ceased rescue operations in Plaquemines Parish, saying it felt confident it had gotten everyone out. There were no serious injuries. National Guard spokesman Capt. Lance Cagnolatti said guardsmen would stay in the area over the coming days to help.

Isaac’s maximum sustained winds had decreased to 45 mph and the National Hurricane Center said it was expected to become a tropical depression by Thursday night, meaning its top sustained winds would drop below 39 mph. The storm’s center was on track to cross Arkansas on Friday and southern Missouri on Friday night, spreading rain as it goes.

Forecasters expected Isaac to move farther inland over the next several days, dumping rain on drought-stricken states across the nation’s midsection before finally breaking up over the weekend.

Even at its strongest, the storm was far weaker than Hurricane Katrina, which at its peak was a Category 5 and hit New Orleans as a Category 3. Isaac came ashore late Tuesday as a Category 1 hurricane, with 80 mph winds near the mouth of the Mississippi River. It drove a wall of water nearly 11 feet high inland. Because Isaac’s coiled bands of rain and wind were moving at only 5 mph — about the pace of a brisk walk — the threat of storm surges and flooding was expected to linger Thursday as the immense system crawled across Louisiana.

In coastal Mississippi, officials used small motorboats Wednesday to rescue at least two dozen people from a neighborhood Isaac flooded in Pearlington. In addition, the National Weather Service said there were reports of at least three possible tornadoes touching down in coastal counties. No injuries were reported.

None of the reports had been confirmed. Until the weather clears, there is no way for survey teams to assess the area to determine whether damage was done by tornadoes or straight-line winds, said NWS Meteorologist Shawn O’Neil.

Back in New Orleans, the storm canceled remembrance ceremonies for those killed by Katrina. Since that catastrophe, the city’s levee system has been bolstered by $14 billion in federal repairs and improvements. The bigger, stronger levees were tested for the first time by Hurricane Gustav in 2008.

In Vermilion Parish, a 36-year-old man died after falling 18 feet from a tree while helping friends move a vehicle ahead of the storm. Deputies did not know why he climbed the tree.

The storm stalled for several hours before resuming a crawl inland, and forecasters said that was in keeping with its erratic history. The slow motion over land means Isaac could be a major soaker, dumping up to 20 inches of rain in some areas. New Orleans reported at about 10 inches in some places as rain continued to fall late Wednesday.

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Contributing to this report were Associated Press writers Brian Schwaner and Stacy Plaisance in New Orleans; Melinda Deslatte in Baton Rouge; Kevin McGill in Houma; Holbrook Mohr in Waveland and Pass Christian, Miss.; and Jeff Amy in Biloxi and Gulfport, Miss.