A reconstructed landscape shows the Shalbatana lake on Mars as it might have looked roughly 3.4 billion years ago. Data used in the reconstruction are from NASA and the European Space Agency. (Gaetano Di Achille/University of Colorado)New images suggest Mars had a sizable lake on its surface billions of years ago, further evidence that the planet had a watery past.

Images snapped by NASA's Mars Reconnaissance Orbiter reveal a 50-kilometre-long canyon, where researchers believe water once flowed, and apparent beach remnants surrounding a basin.

Scientists believe the lake, dubbed Shalbatana for the valley in which it was located, was about the size of Lake Champlain at the United States-Canada border south of Montreal.

The findings were published in this week's Geophysical Research Letters.

Lead researcher Gaetano Di Achille of the University of Colorado at Boulder estimates the lake formed 3.4 billion years ago, an era of the planet that scientists generally have believed was cold and dry. The lake probably evaporated or froze over, he said.

Cornell University Mars expert Jim Bell called it a neat find, but he said he would like to see other data besides images to support the idea there was a lake.

The reconstruction was based on European Space Agency High and NASA MOLA data from the Mars orbiter that show a 50-kilometre long canyon (left). A close-up (right) of the beach-like area outlined in white on the left image indicates the ancient water level. (G. Di Achille/University of Colorado; NASA; ESA)