Near the end of the game you will be destroying the triangles that would electrocute you if you got close to them to restore the ocean. Once you’ve gone through all of them you will make your way out to an open area. In that area directly ahead of you there will be a bigger triangle that you will need to enter to continue to the end of the game. Don’t go into it and just swim down and you will see the blue whales below. Grab onto one of them and ride it to the surface to breach the water. You will see a short animation while breaching the water and you will obtain your trophy.