This image from NASA's Mars Reconnaissance Orbiter (MRO) shows an impact crater looking amusingly like a tadpole because of the valley that was carved by water that used to fill it. It is often difficult to differentiate between inlet and outlet channels, but water always flows downhill. In this particular case, we can infer that water is flowing outward because we have the necessary terrain-height information. When studying these images in detail, scientists can gain a better understanding of the strength of the flooding water that carved the channels, and better understand the history of water activity in this region of Mars.