During the late 19th and early 20th centuries, it was erroneously believed that there were "canals" on the planet Mars. These were a network of long straight lines in the equatorial regions from 60° north to 60° south latitude on Mars, observed by astronomers using early telescopes without photography.

Canals or artificial waterways are waterways or engineered channels built for drainage management or for conveyancing water transport vehicles. They carry free, calm surface flow under atmospheric pressure, and can be thought of as artificial rivers.