The NanoRobotics team at Carnegie Mellon University (CMU) are working on a robot that walks on water, mimicking the Basilisk, or "Jesus Lizard" that's famous for its ability to dash across a water surface on its hind legs. Researchers see amphibious potential in the water-walking robot, as well as a possible efficiency boost in comparison to a boat, because a vehicle that runs across the surface of water experiences very little viscous drag. Computer simulations have been encouraging, demonstrating a few possible efficiency gains in the design and motion over the evolutionary model provided by the Basilisk, particularly with the option of using two or more sets of running legs. Several leg designs have been tested (see one in action in
this video (MP4)) but the researchers are still working on an operating prototype.
The basilisk is well known for its ability to run across the surface of a body of water at a very fast rate of up to 1.5 metres per second. Check out this amusing video of the "Jesus Lizard" in action to see how it manages this. It's distinguished from other water-riding animals and insects by the fact that it doesn't use surface tension to keep it afloat, instead elevating and propelling itself by the slapping motion of its large, webbed feet.
The Water Runner Robot is designed to operate using the same principles. The CMU NanoRobotics research team spent a lot of time studying the motions of the basilisk to learn to mimic and then optimize the water-running motion to generate enough lift and thrust to sustain and move a robot far heavier than the lizard itself.
See the full research paper here (PDF).