|Fig. 1: This image illustrates the process of generating electricity using hydropower plants from initial intake of dam water to electricity transfer through power lines to residential homes. (Source: Wikimedia Commons)|
Hydroelectric power is a renewable energy source that does not consume natural resources to generate electricity. In addition, the energy source does not emit CO2 emissions nor does it pollute the land or water. Hydroelectric power accounts for roughly 96% of the renewable energy in the US. There are 58 hydroelectric power plants throughout the Western United States that generate over 40 billion kWh (kilowatts per hour) per year, powering 14 million people's homes. 
Energy is neither created nor destroyed; it can only be converted. As shown in Fig. 1, hydroelectric power plants harness running water usually from dams. The kinetic energy from the flowing water is converted into mechanical energy, rotating the blades of a turbine. Once the blades are in motion, a generator is activated, converting the mechanical energy into the applicable energy source, electricity.
Most hydroelectric power plants are located in remote areas and must be transmitted to more urban and populated areas. In order to do so, myriad networks of transmission lines have been constructed to bring electricity directly to residential homes and apartments. The electricity generated enters transformers that increase voltage, allowing the electricity to travel through power lines. 
The demand of hydroelectric power alters the amount of water released from a dam, causing fluctuations in stream flow. When demand is high, more water is released. When demand is low, less water is released. Such adjustments in water flow negatively impact aquatic life and water quality including temperature, dissolved oxygen, and turbidity. Also, dams prevent normal fish channels, which can reduce local fish populations. A decline in certain species of fish can result in negative implications for the broader environmental community. Lastly, downstream riverbanks are more likely to erode due to damming for hydroelectric power, altering nearby land ecosystems. 
Although hydroelectric power is a viable renewable energy source that generates a sufficient amount of energy for homes across the US, the environmental consequences are too severe to build more plants. We must focus on improving existing ones to ensure the environment is affected in a minimal way while also continuing to supply billions of kWh per year to American homes.
© Jack Jones. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 "Hydroelectric Power," U.S. Department of the Interior, July 2005.
 D. M. Rosenberg, R. A. Bodadly, and P. J. Usher, "Environmental and Social Impacts of Large Scale Hydroelectric Development: Who Is Listening?," Global Environ. Change 5, 127 (1995).