More than 40,000 homes have been damaged and at least 11 people are believed to have died in historic flooding that has ravaged parts of Louisiana, NBC News reports.

The Coast Guard and Louisiana National Guard were mobilized to help get more than 20,000 residents affected by the flooding to safety, according to CNN. Days after the evacuation, NBC News reports that as many as 8,000 people still remain in emergency shelters.

The flooding was due to an inordinate amount of rainfall. Louisiana's Governor John Bel Edwards has called the rainfall and subsequent flooding “unprecedented,” according to CNN, and the National Oceanic and Atmospheric Administration said the flood is a “500-year flood.” That means that flooding of this magnitude typically happens twice a millenium. Others, such as Brad Kieserman, the vice president of disaster services with the Red Cross, said that the flooding in Louisiana is the worst natural disaster in the United States since superstorm Sandy in 2012.

Though a number of nonprofit relief organizations — such as the Salvation Army, Red Cross and Operation Blessing International — are also helping the military with relief efforts, Governor Edwards called on citizens who wanted to volunteer their time and abilities to help clean mud out of damaged homes, according to CNN.

According to CNN, Louisiana received about one foot of rain a day between Aug. 8 and Aug. 14. That means about 6.9 trillion gallons of water poured from the heavens onto the state. To put it in perspective, CNN says that’s enough water to fill more than 10 million Olympic-size swimming pools.

In light of the scale of the flooding that is taking place in Louisiana, some have asked why such a massive natural disaster isn't receiving as much national attention as it should, according to the Washington Post.

William W. Craig Fugate, administrator of the Federal Emergency Management Agency, addressed this issue and assured residents in Louisiana that the federal government is aware of the situation on the ground, even if much of the American public is not.

“This is a very large disaster impacting tens of thousands of people,” Fugate said at a press conference in Baton Rouge, according to the Washington Post. “Irregardless of what it may be getting in the national coverage, we know this has been a significant impact here in Louisiana.”