Canals are man-made waterways, usually connecting existing lakes, rivers, or oceans. They are used for transportation, often by barges or narrowboats on smaller canals, and by ships on ship canals that connect to the ocean. Inland canals preceded the development of railroads during the Industrial Revolution, and some canals were later drained and used as railroad rights-of-way.
Irrigation canals are man-made waterways for the delivery of water and preceded the use of transportation canals.
Canals on Mars
For a time in the early 20th century, it was believed that there were canals on Mars. This belief was due to a combination of errors: an optical illusion caused the astronomer Giovanni Schiaparelli to think he saw channels on the planet's surface, and the Italian word for channels, canali, was misunderstood by English-speakers.