Hydropower is can be used as electrical or mechanical. It is made by taking water and using it to do useful work. Some of the work that it has been known to do is saw lumber, and grind grain. The water is usally transferred through a variety of ways; shafts, pulleys, wheels,cables and gears. The hydropower dates back to the Greeks who used vertical axis water wheels as early as 85 BC and horizontal axis wheels from 15 BC. The hydropower was the only source besides wind power to do useful work until the steam engine came along in the early 19th century. a lot more cna be found in the book on pages 409-415 Haney