If a tornado moves over a lake, or forms over a lake, it picks up water and can be called a waterspout. However, it is fundamentally no different from a tornado at this point because it draws its violent wind from the highly energetic parent thunderstorm. There is another sort of waterspout which is not associated with violent storms. In relatively warm oceans and large lakes in summer and fall, columns of rotating, rising air often form into a spinning vortex similar, but weaker, than a tornado.
These non-severe waterspouts can be dangerous to boaters, but are not nearly as violent as tornadoes because they are not attached to a violent parent thunderstorm. A similar phenomenon, known as a land-spout tornado, is like a non-severe waterspout except that it forms over land and picks up dust instead of water. Tornadoes, waterspouts, land-spouts, dust devils and cold-core funnels are all results of rising, rotating columns of air. The main difference is that some are much more dangerous than others.