Wikipedia rules
http://en.wikipedia.org/wiki/Bubble_ring
A bubble ring is an underwater ring vortex where an air bubble occupies the core of the vortex, forming a ring shape. The ring of air as well as the nearby water spins toroidally as it travels through the water, much like a flexible bracelet might spin when it is rolled off a person's arm. Some scuba divers can create bubble rings by blowing air out of their mouth in a particular manner. Long bubble rings also can form spontaneously in turbulent water such as in heavy surf. Bubble rings and smoke rings are both forms of vortex rings, and are sometimes studied in the field of fluid dynamics. Dolphins and humpback whales have also been seen to create bubble rings. Dolphins sometimes create bubble rings on purpose, seemingly for amusement.