Film set mainly in the ocean with a mixture of live action and animation

Hello,
I am looking for the name of a film that starts with a view of a beach with beached whales and then the action follows the main character swimming in the ocean.
It’s a film that mixes live action and animation if I remember correctly.
It must be from before 2008, I watched it as a youngster.
If anyone can help me, I can’t thank them enough
Apeth