I've dealt with things that live underwater before, and...they're not something you want to face by yourself. This might not be anything, or it could be something other than what I'm worried about, but...
If it is the things I'm thinking of, it's very, very dangerous, Ava. I hate even typing the names of these things, but if you've ever heard of the Necronomicon, or Dagon, or R'lyeh...you're on the right track.
I don't want you going by yourself. We'll both go, but I'll need a little time to prepare some...equipment.