Researchers analyze Lagrangian coherent structures in water around swimming fish

Fish may seem to glide effortlessly through the water, but the tiny ripples they leave behind as they wriggle their way along are evidence of a constant give-and-take of energy between the swimmer and its aqueous environment--a momentum exchange that propels the fish forward but is devilishly tricky to quantify because of the continuous nature of a large, ever-flowing body of water.