I thought books on marine life / sea creatures would be extremely common, but after visiting three Barnes & Noble and Borders shops, I was surprised that I could not find a book that was scientifically-accurate yet engaging for my 6-year-old niece.
The book is well laid out, with large, detailed and life-like drawings of the sea creatures [See the picture I uploaded, with notes]. The descriptions are slightly complex for a young child, which I think may be more suited to say, an average 12-year-old to fully comprehend on their own. That said, I believe a child of as little as 4-years-old would be able to appreciate the pictures, and also the interesting trivia about each creature, if read-to by a grown-up.
The author also works in additional information such as sustainability (brief notes about tuna stocks being overfished, for example), environmental issues (pollution and its effects on marine life) and other human factors (finning of sharks). I am glad that the book introduces these issues in an objective manner which helps raise awareness in children.
The book is not hardcover, but the cover is fairly rigid and seems water-resistant. The inside pages are also smooth to the touch and seem 'coated', instead of just regular thin flimsy paper.
I would HIGHLY recommend this book and am even considering getting the others in the series (insects, birds etc).