More than 500,000 people were without power in Louisiana because of Hurricane Ida, Entergy Louisiana's website showed on Sunday.
The energy company's outage map showed the number of affected customers at 541,606 as of 6:50 p.m. EDT on Sunday.
Hurricane Ida made landfall in Louisiana on Sunday as an extremely dangerous Category 4 storm, forcing those who did not flee to brace themselves for the toughest test yet of the billions of dollars spent on levee upgrades following Hurricane Katrina 16 years ago.