Akishima Laboratory (Mitsui Zosen) have created the most literate kiddie pool ever:
The device, called AMOEBA (Advanced Multiple Organized Experimental Basin), consists of 50 water wave generators encircling a cylindrical tank 1.6m in diameter and 30cm deep. The wave generators move up and down in controlled motions to simultaneously produce a number of cylindrical waves that act as pixels.
I imagine that these wave generators synchronize their movements so that each circular wave peaks at the point where the "pixel" is desired. Add enough of these waves, all firing at the same time, and they can create shapes (that appear for a split second). It's not like the Abyss creature, but with a new pattern able to be generated every three seconds it would probably be fascinating to watch.
(via Pink Tentacle)