Dolphins at Daybreak
Mary Pope Osborne
Jack and Annie are so excited when the Magic Tree House carries them off to a sparkling coral reef, and they get to go exploring in a mini submarine. There are wonderful creatures everywhere, and Anie makes friends with a pair of dolphins. But the ocean is dangerous and there’s a shark down there.
Reviews

excellent
Anonymous 08.09.2015

It tells you about sea creatures.
Anonymous 19.08.2015