The heaviest animals known to run on water pull off the feat by using quick strides and large feet that slap the surface.

Credit: Susan Bissell

Western and Clark's grebes (Aechmophorus occidentalis and Aechmophorus clarkii; pictured) run as far as 20 metres on water and for up to 7 seconds during a mating ritual, and are among only a few animals with this ability. Glenna Clifton at Harvard University's Concord Field Station in Bedford, Massachusetts, and her team analysed high-speed video of wild birds performing the dance and studied models of the grebe foot in the laboratory.

They found that the birds stay above the water by having a fast stride rate of up to 20 steps a second, as well as wide, flat feet that slap the water surface with enough force to support up to 55% of the bird's weight. The animal's feet are also shaped to reduce drag.

J. Exp. Biol. 218, 1235–1243 (2015)