Check out this video of an archer fish (Toxotes jaculatrix) shooting down prey by creating a water jet:
Here it is again in slow motion:
Until now, the mechanism by which the archer fish produces such a powerful jet of water was a mystery. Contrary to prior hypotheses, the fish do not have specialized internal structures. Dr. Alberto Vailati and colleagues at the University of Milan filmed the fish and found that the initial jet of water travels at an impressive 2 meters per second and the lagging end of the water jet is actually faster. The end result: the head of the water jet is held together by surface tension such that as the speed increases, it packs a punch that knocks down prey into the water for the fish to eat.
Source:
Nature, doi:10.1038/nature.2012.11668