A storm transformed part of the Mississippi Delta into "an ocean", according to Mississippi governor Phil Bryant.
It also left parts of Louisiana with 43 cm of rain.
More than 90 people across 11 parishes in the area were rescued because of high levels of water.
Many expected the storm, previously categorised as a hurricane, to cause more damage than it did.
Fears circulated prior to the downpour that some of Mississippi River's levees would be toppled at New Orleans, allowing the canals to rush into the city. This destruction happened before, in 2005's Hurricane Katrina, with devastating consequences for the city.
A shift in the hurricane's path, however, decreased the likelihood of this outcome, with lower levels of rain seen than forecasters had predicted.
No casualties have been reported as a result of the storm.
“This was a storm that obviously could have played out very, very differently,” said Louisiana governor, John Bel Edwards. “We’re thankful that the worst-case scenario did not happen.”
More than 325,000 power cuts took place over the course of the storm, spanning multiple states, estimated the Edison Electric Institute.