I wanted to reinforce this subject of this movie, it really is a joy to see. Get a copy or rent it for your kids, grandkids, etc. Guarantee they will love it
And here is an article on how they constructed the mechanical dolphin that was needed as a stand-in.
About the robo dolphin
The robotic dolphin was needed as a stand-in for Winter in sequences that would either be too dangerous or difficult, or that could exhaust the real, recovering dolphin. KNB needed to mimic the size, coloration, and water retention of the real dolphin in addition to mimicking its fluid motions. Because the movie needed shots both in the water and at the surface of the water, a full-scale dolphin robot with internal electronics and actuators was used. This eliminated the strings often used with puppets, which would be harder to process out due to their effect on the water surface. Robotic dolphin for the movies