SOLVED. YA Fantasy/ Sci-fi. Kid discovers that whales are submarines for an underwater whale civilization. [s]

[Brady]

I read this book 5 years ago in 2016 and it seemed relatively new then. I remember there was an orca named Kevin. The kid (I can't remember if it was a boy or girl) rides inside the whale submarine after befriending some whales and learning the secret truth about them. And the kid gets to visit the underwater whale civization where the "whales" come out of their whale bodies and walk around and live in buildings that they made out of some squishy material. I think the kid's parent was a whale researcher and they lived on some island.
I remember the cover being very minimalist deep blue. I think it was a one-word title.

[Mai]

This one that came up searching online sounds close! It's Fluke: Or, I Know Why the Winged Whale Sings by Christopher Moore. Several readers' reviews mention that all the killer whales are called Kevin.

[Brady]

That's it! Thank you! :D