What's the Name of That Book??? discussion

I read a book and I cant remember any names but the story is haunting me right now so I have to know. There are these sisters (I think they were twins) and they lived in this underwater city. There is priests in a kind of church in the centre and they take care of the bats there because there are no other animals in the city so they are seen as holy. their mother was a high priest but died. the outside world is thought to be toxic but they cant have too many people down there so only one child from each family can stay and the others must go to live on the surface going up this elevator thing. The main character finds out that the other priests killed her mother and that they know the outside world is safe now but keep people down there. There was also something about her learning swimming, bats dying and hearing a sort of siren voice. Her older sister says that she will go up so main character can stay safe but main character doesn't want to because she known the secrets and that the priests will kill her next. They somehow both end up on the surface and the surface people immedietly try to kill them because they don't trust the priests who have been trying to do something shifty up there. I can't really remember the ending that well, please help!

Atlantia by Ally Condie?

Becca wrote: "Atlantia by Ally Condie?"
YES!!!! Thank you that was so quick!