(CNN)—Saturday marked the fourth anniversary of Hurricane Katrina.

In New Orleans, residents are remembering the devastating storm and the breach of the levees with a ceremonial bell ringing service.

Mayor Ray Nagin spoke at this morning’s event.

“To all of you who are here today I say thaink you thank you for backing up our city,” said Nagin. “Four years ago, some said it wasn’t worth investing to in our city, [it] didn’t deserve to come back. But you knew better and you came back. Now we stand back four years after that event 80 percent of the city back our population back.”

There are several events happening in and around the city to mark the anniversary, including a 24-hour build-a-thon in Saint Bernard Parish and an outdoor festival in Congo Square.