This review is based on an e-galley provided by the publisher through NetGalley. The following review was originally posted at Lone Star on a Lark. 
 Well, it reads a bit like Little Mermaid fanfic, especially at the beginning. I mean you can practically see the scenes happening in bright, cartoony animation (which is not too far off the mark considering this is a Disney book for Poseidon's sake). But I made the choice not to let that bother me, and anyway the feeling of fanfic-ishness doesn't really last past the first few chapters. 
 For the most part, the unique physics and cultural stuff of this underwater world are pretty consistent. There is one scene in which a character gets a very funky haircut that I just could not picture happening underwater at all, but I think other than that all of the little details were pretty well done. I'm thinking particularly of a mention of buoyancy problems in freshwater as compared to saltwater, which made me think far too much about the osmoregulatory abilities of mermaids. 
 There's lots of fun but sometimes too-cheesy mermaid slang (which undoubtedly would be called merlang, har har har). Plus I have to praise the weirdly delicious descriptions of otherwise gross-sounding seafood candies. And I liked this inclusion of different types of mermaids -- classic sparkly scales, lionfish-like, eel-like, orca-like, even bioluminescent (LOVE). Of course, this brought up more questions on the speciation of mermaids (because once a biologist always a biologist) but the backstory of the mermaids in the book is that they were created by a goddess during the fall of Atlantis, so whatever. 
 Oh and I hope the finished book gets a map. I could have really used one because I had a lot of trouble picturing just where everything was taking place, but the e-galley didn't include one. Apparently Disney is planning an illustrated gift version as well as graphic novels based on this series, so I don't think a map is too much to ask for. 
 There were some signs of an impending love triangle, but either that's going to come up again in some future book in the series (and, yes, this is the first of a series) or it was wisely given up in favor of sisterly bonding between girl - sorry, merl - friends... or it is a TRICK and one of the boys involved is not whom he seems, which is my bet, and I am going to feel SO SMUG if my guess turns out to be right.