Phenomenon is called Karman vortex. In this particular case the spinning air effect was caused by pressure difference (vacuum) created by rapidly spinning water, which "sucked in" air. The vortex continued to grow till the water had momentum, or till it reached the ground. Low pressure area continued to grow with the vortex. After the vortex stopped growing, it continued to spin, until its centripetal force was too weak to compensate the buoyancy of air bubble.
This phenomenon is created by hydrofoil all the time. More speed = more momentum to the spinning water. In this case, first vortex was created very close to the water surface, so the vacuum was able to suck in air.
In this example
[youtube]http://www.youtube.com/watch?feature=pl ... -THVj7GeXs
you can see creation of 2 vortexes. Case is very simillar, only here two vortexes were strong enough to suck in air.
If some sort of dye were in the water, you could see those vortexes being made all around the trajectory of hydrofil´s neck.
And NOT only, this exact phenomenon is, what causes kite lines to drag, and flags to flap.
Conclusion: more round is the neck of hydrofoil, more drag in the form of Karman vortex is present