Flood waters receded in much of southern Louisiana on Wednesday, after a days-long deluge that inundated vast areas, claimed at least 11 lives and impacted some 40,000 homes.

Residents were cleaning up and trying to assess the scope of the devastation left by unrelenting rains that overwhelmed rivers and sent them flooding into residential areas.

"Right now, in our neighborhood it feels like we had an atomic bomb go off," said 57-year-old Sonya Sims, who described an area where every home had flooded.

Her family has owned her home in Denham Springs - a city of 10,000 east of the state capital Baton Rouge - for 65 years. She expects it will be torn down.

"Today, we just pulled everything out that we could, and stacked it up, and sorting through the rubble to see what we can find to save," Sims said.

The most cherished possession she saved were childhood photos of her two children, Sims said.

While many areas were drying out, the National Weather Service forecasted that all waterways would not fall below flood stage until as late as Friday.

"There's still record flood water," Louisiana Governor John Bel Edwards told local news media while touring disaster areas. "I don't want anyone to think that we turned the page."

Rescue crews were still going to every home and flooded car they could reach, to check for bodies or survivors.

The confirmed death toll remained at 11 on Wednesday.

In places where residents were able to return to their neighborhoods, they were salvaging what they could and gutting their homes in a race against mold.

In Walker, a town of 6,000 people east of Baton Rouge, heaps of belongings were outside waterlogged homes. Scrapbooks, television sets, furniture, dry wall, carpeting and insulation were strewn on front lawns.

President Barrack Obama has declared 20 parishes disaster areas - freeing up federal money to aid victims.

Sims is among many without flood insurance who will depend on federal assistance.

More than 70,000 people had already registered for help, according to White House Deputy Press Secretary Jen Friedman.

Secretary of Homeland Security Jeh Johnson planned to travel to Louisiana on Thursday to review recovery efforts.

"Well over 75 percent of our parish has been touched by this," Sheriff Jason Ard of Livingston Parish said during a Tuesday news conference. His parish is home to more than 130,000 people.

"It is something that is going to take months upon months to recover from," Ard said.

The scope of the disaster meant the wait for home inspections alone could be days, if not weeks.

The American Red Cross launched a donation campaign for flood victims, and deployed 67 emergency response vehicles, according to spokesperson Patrick Pannett who was interviewed by local TV station WAFB.

"We're going to have thousands of people coming in," Pannett said.

The Salvation Army was also collecting supplies and singer Taylor Swift donated $1 million, saying the disaster was "heartbreaking."