https://www.vice.com/en_us/article/5dbq5z/lakes-on-mars-may-be-a-mirage-scientists-say

Water is the key ingredient for life on Earth, which is why scientists hoping to find aliens on other worlds are particularly interested in its presence. A team of researchers made a huge splash on this front in 2018 by suggesting that radar observations of bright patches under the southern polar cap of Mars were hidden lakes that could potentially provide a habitat for modern Martian microbes, according to a study in Science.

But a trio of new studies throws cold water on these hypothetical subglacial lakes by proposing alternative explanations for the observations, which were captured by the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument on the European Space Agency’s Mars Express orbiter.