Hydropower is also sometimes called water power, and is basically a power that is coming from the force or energy of moving water. Hydropower offers some advantages over some other energy sources but there are also some disadvantages that should also be mentioned. Let's start with advantages.
The first thing you need to know is that hydropower is clean, renewable energy source that doesn't pollute our planet with harmful CO2 emissions like burning of fossil fuels does. Though hydropower doesn't cause air pollution, and doesn't contribute to climate change problem like fossil fuels do, hydropower is not totally environmentally acceptable energy source but I will tell you more about this later in the article.
Hydropower is much more stable (constant) source of energy compared to wind power and solar power because once dam is complete, electricity can be produced at stable rate. Also, when demand is not high it is easy to stop electricity generation, and "plug it in" once again in times when demand increases because water can be easily saved for use when needed.
Once dams are built they are not only highly efficient but they are also designed to last for a very long time, with relatively low operational and maintenance costs. Hydropower is in fact among the most reliable and most efficient renewable energy sources that ensures constant supply of electricity in many parts of the world.
Hydropower can also contribute to economic growth of area where hydropower dam is built because the lake that forms behind the dam is not only often used for irrigation purposes but also for recreational tourism in form of water sports, fishing, swimming, boating, and some other recreational benefits. At the end I will also mention that hydropower does not produce waste like some other energy sources (most notably fossil fuels and nuclear power) do.
When there is talk about the disadvantages of hydropower many people think of environmental damage that can happen as the result of dam building. For instance hydropower dams can disrupt the natural flow of rivers which can have negative impact on many river ecosystems. If really large hydropower dams are built then this can lead to earth quakes, erosion, landslides and serious geological damage (this was the case with building of the Hoover Dam in the USA, and with building of the Three Gorges Dam in China). It can also lead to flooding, and sometimes people have to even leave their homes (this was the case with Three Gorges Dam that displaced some 1.24 million people because of serious flooding). Building hydropower dam can also change stream levels, flow patterns, temperature of the water, all of which can have very harmful effect on wildlife.
Hydropower disadvantages from economic point of view include huge initial costs to build the hydropower dam, meaning that hydropower construction must operate for at least couple of decades before start bringing profits. Also, in times of droughts when there is not enough available water, hydropower cannot produce electricity.