I'm trying to identify a sci-fi graphic novel set underwater

I haven’t read this story in ages, but I recently remembered it and couldn’t find it on my bookshelf.
I’m not sure if it was originally a graphic novel or a comic series which was reprinted as a trade paperback.
I do know that it’s from a western setting as the pages were ordered from left-to-right, and it was printed in A4 rather than your regular sized book.

The plot, as I remember it, revolves around one woman and a race war between some fish people and humans. She was hired to work in some deep-sea lab (like a series of domes) when the fish people attacked.
It’s around this time we find out that she is part fish-person, or is one of the fish people (to be honest, the details are rather fuzzy).

I remember one scene, in particular, that might help with identifying the book.
After the attack on the deep sea lab, the protagonist is rescued and sent to the hospital where they (the military doctors maybe?) discover she has a lung capacity 4 times that of an Olympic swimmer. That’s the only part I remember really clearly, the 4 times lung capacity part.

Any help in finding this would be greatly appreciated.