New high-resolution satellite images reveal features on the planet's surface which change during different seasons, indicating water that flows in a liquid form. The streaks the size of a football field appear on the sides of craters and canyons and indicate salt deposits left by water flows.
Scientists revealed the highly anticipated news after teasing an announcement in which it would "solve the mystery of Mars".
The images from NASA's Mars Reconnaissance Orbiter provide the strongest evidence yet of flowing water. The streaks darken during warm periods - where temperatures are above minus 10 degrees - and fade as it gets cooler and appear at several locations.
The salt lowers the freezing point of the water, they suspect.
"Our findings strongly support the hypothesis that recurring slope lineae form as a result of contemporary water activity on Mars,"scientists concluded in Nature Geoscience journal.
"Water is essential to life as we know it. The presence of liquid water on Mars today has astrobiological, geologic and hydrologic implications and may affect future human exploration."
There is a greater chance of microbes existing in flowing water than when it is in other states such as ice. The researchers have not identified the source of the water flow, however.
"Our quest on Mars has been to 'follow the water,' in our search for life in the universe, and now we have convincing science that validates what we've long suspected. This is a significant development, as it appears to confirm that water - albeit briny - is flowing today on the surface of Mars," said John Grunsfeld, an astronaut and associate administrator of Nasa's Science Mission Directorate in Washington.