A team of researchers led by Roberto Orosei of the National Institute for Astrophysics in Bologna, Italy, surveyed a region called Planum Australe, located in the southern ice cap of Mars, from May 2012 until December 2015.
"If there is actually a substantial liquid water reservoir or aquifer of some sort, I think that definitely increases the chances of life on Mars - bacterial or microbial life", said Mickol, now a postdoctoral fellow doing research at the Naval Research Laboratory in Washington, D.C.
What is believed to be liquid water is sitting below Mars' southern polar ice cap and is described as a "well-defined, 20-kilometer-wide zone".
They obtained 29 sets of radar samplings, mapping out an area exhibiting a very sharp change in its associated radar signal, about 1.5 km below the surface of the ice and extending sideways about 20 km.
Scientists still don't know just how much or how deep the water is on the planet.
Orosei said the water in the Martian lake was below the normal freezing point but remained liquid thanks in large part to high levels of salts.
If that is how it is then it would be the first confirmed news of liquid water ever detected on the Red Planet.
Scientists have uncovered a "a stable body of liquid water" on Mars, in what some are calling a "game changer" in the search for alien life.
Life on Mars? Liquid water lake found on the Red Planet
The location's radar profile resembled that of subglacial lakes found beneath Earth's Antarctic and Greenland ice sheets.
A few years ago, biologists found more than 3,500 unique gene sequences in Lake Vostok which had been isolated for more than 15 million years; Lake Vostok gets no sunlight with it being 4,000 metres below the ice and has a recorded temperature of -89.2c, showing life to be hardy.
The ISA team's findings will appear in this week's issue of the journal Science, they will reignite speculation about the planet's geology and the potential for life on Mars. There had been some signs of liquid water now on Mars, including disputed evidence of water activity on Martian slopes, but not stable bodies of water.
The tool is called the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS), and was created to find subsurface water by sending radar pulses that penetrate the surface and ice caps.
Lake beds like those explored by Nasa's Curiosity rover show water was present on the surface of Mars in the past. After that, the discovery of a liquid lake is groundbreaking news.
The discovery is the latest of many breakthroughs by Nasa's Mars missions.
"We found that any other explanation for these very strong echoes was not really tenable in light of the evidence that we had available", he said. When they found evidence of the subterranean lake, they were careful not to jump to conclusions, the scientists told NPR.