Bacteria swimming in flowing water are shown in this diagram of a mathematical model of their motions by the researchers. The background colors show the orientation of the cells’ long axis (horizontal axis) and their position across the width of the stream (vertical axis). Superimposed on that are two representative examples of bacteria, showing their changing orientation, and revealing that they spend much more time aligned with the flow (horizontal) than perpendicular to it (vertical). Image courtesy of the researchers