That erroneous idea, that there are "canals" on Mars came from the descriptions of the Italian astronomer Schiaparelli, who of course, spoke Italian and called them canali, meaning "channels" (not the mascarpone filled dessert, you chowhounds) and English speakers took off too far with the term. "Canal" implies an artifice, a man-made channel, whereas this latter term is more general and includes natural formations.
Open channel D, open channel D.
This is absolutely true, but further more, even these "channels" were later identified to be optical illusions. There are no channels or canals on Mars at all.
The science fiction writer, Edgar Rice Burroughs took up the theme of canals on Mars and wrote a series of books about Martian adventures that became popular at the time. They were written from 1917 to 1964, 11 books in all, and he is often compared with H.G. Wells and H. Rider Haggard. Burroughs is most well known for the creation of the character Tarzan who featured in 24 of his novels.
It is well known today that there is in fact a huge amount of water on Mars. Most of it is locked up as frozen ice mixed in with dry ice (drozen carbon dioxide) in the polar regions of the planet. It is also thought that a lot of of frozen water ice is buried in the permafrost of the surface and were all the water to melt on Mars, it would create a planet wide ocean 13 kms deep.
The temperature on Mars ranges from -200C in winter to a balmy -20C in summer. Flowing liquid water, id therefore, not an unreasonable prospect to have occurred on the surface of the planet, especially in its past when the planet was warmer.