When you spend your life in the water, you tend to develop a good intuition for its subtleties. Dolphins have been observed creating bubble rings by, among other techniques, carefully exhaling air in the middle of the vortices caused by the motion of their fins through the water.
Besides being fun to watch and an impressive demonstration of fluid mechanics, the phenomenon may throw some light on dolphin cognition since the skill to create the rings is subtle and tends to be passed from one dolphin to the next by careful observation and practice.
Also intriguing is a report that dolphins appear to be using sonar to locate the vortex in the water, an impressive feat of audio analysis. More
Scuba divers have long blown bubble rings for fun, watching them rise to the surface. Some I know are quite good at it although I’ve never quite grasped the technique. But dolphins have learned to control the direction of their rings and even divide them into smaller segments. It’s fun to watch them at play!