John Bacon

USA TODAY

Historic flooding that killed six people and forced more than 20,000 sometimes harrowing rescues continued to sweep across southern Louisiana on Monday as the region braced for ever higher waters.

More than 12,000 people were staying in shelters and 40,000 homes and businesses were without power, Gov. John Bel Edwards said Monday. The Amite River, one of several rivers and creeks that poured over its banks, crested Monday in Baton Rouge but was still rising south of the capital, the National Weather Service said.

"These rivers won't recede below their banks for a few days, and it will take several days for waters to recede," National Weather Service hydrologist Jeff Gaschel told USA TODAY.

Parts of southern Louisiana and Mississippi were hammered by up to 25 inches of rain late last week. The sun re-emerged Monday, but water was everywhere. And the threat of showers remained.

President Obama has signed a disaster declaration, and Edwards said that up to 30 counties could receive the declaration before the disaster has passed. Hours later, more than 11,000 people had registered for aid, Edwards tweeted. The available aid includes grants for temporary housing and home repairs not covered by insurance as well as other grants and loans.

Here's how much rain fell in Louisiana

In Ascension Parish, about 25 miles south of Baton Rouge, a convention center was playing host to almost 600 people chased from their homes. Parish homeland security official Meredith Conger told USA TODAY more were expected in coming days.

Conger, in need of baby formula and other essentials, put out a call for help. The community responded.

"We are getting what we need," Conger said. "It's a disaster and everyone wants to help. We have some great people here."

Unusual meteorological phenomenon to blame for La. flooding

Volunteers with boats aided the rescue effort, too. In St. Bernard Parish, Jared Serigne told the Associated Press he helped organize volunteer efforts involving roughly 70 experienced boaters who navigated through unfamiliar waters to rescue hundreds from flooded communities.

In Baton Rouge, lawyer Jamie Flowers said he went to bed Saturday night with no power but no flooding, either. He woke up Sunday to bright sunshine and water up to his porch. His neighborhood streets were flooded. He and his 2-year-old daughter, Mattie, were stranded.

Flowers told USA TODAY he called 911 but was told they were not a priority. Finally, a Facebook post did the trick: "If anyone is out and about rescuing folks or knows someone who is rescuing, please send them this way."

A short time later someone with a boat knocked on his door.

"They didn't even know us, they just pointed to the post and said 'Is this you? We're here to rescue you,'" Flowers said. He was reunited with his wife and two other children at her mother's home, but never did find out who his rescuers were.

Flowers hasn't been able to return to his home yet, so he doesn't know if the water has risen or fallen.

"I just hope we are not in six feet of water," Flower said. "But we are safe."

There were other victories. More than 1,500 motorists stranded by high water on I-12 near Covington were all rescued by Sunday night, some after spending more than 24 hours on the highway. Many vehicles remain abandoned on the highway.

The U.S. Coast Guard on Monday said its crews had rescued a total of more than 195 people and 26 pets — and assisted more than 2,900.

Some neighborhoods were overwhelmed in water, but others nearby were spared. Scott resident Will Mitchell said he believes some newer subdivisions suffered due to a lack of proper drainage. But despite almost two feet of water surrounding his home, Mitchell believes he and his family are among "the lucky ones” who will avoid major suffering.

“I’ve lived here my entire life, and I’ve never seen anything this bad come from a rain storm," he said. "Each year it just gets worse, but for us, this is just more of an inconvenience. We got lucky, because we’re safe and our house is safe."

Late Monday, a Louisiana firefighter assisting with rescue efforts accidentally shot and wounded another firefighter, officials told KSLA-TV. The victim's condition was not immediately available.

​Parts of southern Mississippi also were swamped. The Mississippi Emergency Management Agency reported 71 homes damaged, primarily in the towns of Crosby and Centreville. Dozens of people remained in a shelter in Natchez. Gov. Phil Bryant declared a state of emergency for Adams, Amite, Pike, Wilkinson and other counties affected by flooding.

The vacation rental website Airbnb on Monday said it had activated its disaster response tool to help hosts offer their homes free of charge to victims of the Louisiana flooding. The site said users began the service after Hurricane Sandy in 2012.

Wendell Pierce, an actor on The Wire and Treme, had his home destroyed by the flooding in Baton Rouge, 11 years after his childhood home was ravaged by Hurricane Katrina, AP reported Monday.

Bacon reported from McLean, Va. Contributing: Jordan Allen, The (Alexandria, La.,) Town Talk; Greg Hilburn, USA TODAY NETWORK Louisiana