Scientists already had an inkling that water helped form the landscape on Mars, but they're now ready to confirm that claim. In a report written for Science, researchers state that the smooth, rounded shape of the Red Planet's pebbles and the way they overlap is identical to the gravel formation found in Earth's rivers. They appear to be too large to be blown by wind, and their varied shades indicate they were transported from various locations -- telltale signs of a former stream. "For decades, we have speculated and hypothesized that the surface of Mars was carved by water, but this is the first time where you can see the remnants of stream flow with what are absolutely tell-tale signs," said Rebecca Williams to the BBC. This isn't the first time we've heard of water on Mars, but the idea of a Martian river does make us wonder if Marvin had a favorite fishing hole.