Although hydropower has been in use for centuries, largely in the form of water wheels, hydroelectricity is a more recent phenomenon. Hydroelectricity is a type of hydropower and is created as moving water powers machines that produce electricity.

The first hydroelectric power plants were built at the end of the 19th century. By the middle of the 20th century they were a major source of electricity. Today hydropower is the most widely used source of renewable energy making up seven percent of U.S. power production.

The most common form of hydropower comes from hydroelectric dams. Typically, a river is blocked by a dam to create a large reservoir of water. The water from the reservoir is allowed to flow over the dam in a controlled way. As the water falls it turns turbines and generates electricity.

Click on the text boxes above to learn how hydropower dams work.

The U.S. constructed thousands of dams to generate power during the Industrial Revolution. Many hydroelectric dams have survived today but environmentalists have voiced concern over ecological damage and harm to fish and other animals.

A dam building era has given way to an era of dam removal. The largest dam removal project in the U.S. is underway in Washington where the Elwha Dam is being deconstructed on the Elwha River.

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How Hydropower Dams Work 18 December,2015QUEST Staff

  • Matt Stoecker

    I hope Quest includes the real truth about dams in this and future dam discussions, their high greenhouse gas emissions, and negative impact on climate change. Please see the studies below that show why dams are neither a “renewable” or “clean” source of energy when ecosystems and climate are considered.

  • John K Johnson

    The statement “The force of the water spins a turbine at low
    speed–this allows fish to pass through unharmed” is seldom accurate. I wish it were. Turbine mortality is a major issue for fish passing through dam conduits. Its extent depends upon the relative length of the fish compared to the size of the mechanical machinery, the turbine’s rotational speed, the type of turbine, and other factors. Additionally, once fish exit the turbine below the dam they can emerged dazed and become easy prey to birds, fish-eating fish, marine mammals, etc. There is ongoing research into less-lethal turbines (I like that term better than “fish friendly”–there is nothing “friendly” about going through a turbine rotating at high speed!) See These have bigger openings with different geometry and slower rotational speeds than historic turbines. We are hoping these develop into useful means reducing the interaction. Another approach is to shunt fish around the most harmful features at a dam, avoiding turbines entirely.

    Typically overlooked like the proverbial bull-in-the-china-closet are the associated reservoirs that often a bigger problem for fish than the dams themselves since they can change a flowing river in which fish are well-adapted into a quiet pool where non-native predators lurk. This is a particular problem for fish with little motility (juveniles, larval stages) that have no way to hide or escape from predators.

    A lot of discussion abounds about developing novel ways to save the fish at dams. Actually, the discussion and enormous expenditures is primarily about saving the dams, showing people that dams and fish can co-exist. People have an emotional connection with the land and its biota, and will go to great lengths to protect it. They also like to turn on the lights, and loath difficult choices.

    John K Johnson
    Past-President (2011-2013), Bioengineering Section, American Fisheries Society



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