Are underwater tornadoes a regular ocurrance?

Technically, there is no such thing as an underwater tornado. By definition a tornado is a violently rotating column of air. A vortex underwater is called a whirlpool. Whirlpools are not like tornadoes, however. They are not nearly as violent and are usually harmless, though some stronger whirlpools can pose a threat to swimmers and small boats. Natural whirlpools can be observed in streams and at some tidal inlets.