50% repetitive filler, 50% build up to a climax that gets resolved in a sentence. 
The characters are all over the place, constantly changing their beliefs and stances to whatever fits the dialogue Grant feels like writing in the moment. 
Several characters flit back and forth between wanting to drive the mermaids into extinction and wanting to protect them at all costs, without any reasoning whatsoever. One character changes her stance on this at least twice in a single conversation.
Almost every plot point and conversation is dragged out and repeated.
It's obvious that this was written with a sequel in mind. If there is one, I will not be reading it. I don't think I'll pick up anything by this author again. 
There is a lot of disability representation in this book, but it leaves a lot to be desired. Grant focuses on the disability of the characters at the expense of the characters themselves. The two deaf characters especially. They are infantalized at every turn, not just by other characters, but also the narration. I don't think there is a single line about them that is not about them being deaf.

One of the two is the first to die within the main story. The other disappears for almost the entire book, only to be brought back into the story because her deafness makes her scream sound different and it confuses the mermaids.

This book is incredibly mediocre and I would not recommend it to anyone.