This book would be from the 1980s or earlier. I believe the main character was a woman. They are on another planet covered mostly or fully in water. Not entirely sure of the plot. Whales and dolphins could "talk" with people and helped them on this planet.
Dolphins were more child-like and the killer whales were more mature. The larger the whale the smarter and more independent they seemed to be.
At the end, if I recall correctly, one of the blue whales learns to take flight.