Someone recently suggested going back to old favorites as a pleasant little reading vacation, which made me think of a handful of books that I loved when I was a teen and haven't read since then. At least one of which I can't remember the title. Maybe you read it and remember it?
It was a book about two young teens who learned that they were wizards, and in order to save the world (?) they had to learn to turn into whales and dive deep into the ocean to ... ? I don't really remember the rest.