This form of renewable energy, which draws power from slow water currents, was inspired by the movement of fish. The energy can be captured as water flows past a network of rods. Eddies, or swirls, form in an alternating pattern, pushing and pulling an object up or down or side to side to create mechanical energy. It works in the same way that fish curve their bodies to glide between the vortices shed by the bodies of the fish in front of them, essentially riding in each other's wake.