It's a manga created by an independant artist through TokyoPop.
Allow me to explain:
The story is a love story of sorts, a classic one at that. The art is beautiful and very much suited for younger audiences, (The book itself states 8-12) but that's not to say you wouldn't enjoy it either.
The characters are well develop(ing)ed and sweet, plus the underwater environment is refreshing too.
I really feel that this author deserves some publicity, as she is quite good. (And only 23 years old, for you aspiring manga artists.)
http://www.seaprincessazuri.com/azuri/ is her website.
Now for you skittish types, I will mention that the characters, while very much decent, are also shapely. Which equates beautiful, but nonetheless.
Worth a look.