Water is the basis of all living things on Earth. It not only supports life, but it is also used to generate electricity everywhere around the world. Although hydroelectricity is one of the oldest sources of energy, it is still a source that is clean and beneficial to the environment. As stated by the Wisconsin Valley Improvement Company (WVIC), approximately 20% of all electricity is generated by hydropower, worldwide. Unlike fossil fuels, hydroelectricity is a low-carbon energy and a renewable resource that is a solution to the pollution problem that is occurring on Earth. Hydroelectric power plants have been created and used all around the world to reduce carbon dioxide emissions. Fossil fuels are pollutants that release large amounts of greenhouse gases into Earth’s atmosphere. However, to produce low-carbon energy, carbon-based energy must be used. With the expanding global population and the increasing need for energy, carbon-based energy must be used to produce low-carbon energy to solve this problem. A hydroelectric power plant has three main parts; an electric plant where the electricity is produced, a dam that can be opened or closed to control water flow, and a reservoir where water can be stored, (National Geographic, 2009). The water is first stored behind a dam in a reservoir and when the dam opens, the moving water has gravitational potential energy and is converted into kinetic energy as it runs down the pipes to turn the turbine. The turbine is connected to a metal shaft that moves into an electrical generator which allows the kinetic energy to convert into electrical energy, (BBC, 2014). The generator is connected to power lines to carry electricity in homes and buildings. The amount of electricity that can be generated through water depends on the volume of water and its speed, (Government of Canada, 2017). Hydroelectric power plants are usually built in water bodies where there is a sharp incline to take advantage of the speed gained by the water from gravity, (Government of Canada, 2017), such as the iconic Niagara Falls. Wherever there is a large drop in elevation, there will be a high pressure when the water arrives at the turbines to create a large amount of energy. The waterfalls in Niagara Falls have a large volume of water that falls with a high pressure that can generate a high amount of electricity. In addition, hydroelectric power plants would need a high level of technology and the large supply of rivers. According to the data collected by Energy Information Administration, in 2012, China lead the world in the most produced hydroelectric power with 856.35 billion kilowatt hours. It was more than double the amount by the second place country, Brazil, which was 411.19 kilowatt-hour. Followed by Canada with 376.71 kilowatt-hours, and the United States with 276.24 kilowatt-hours. Hydropower is produced with an average of 0.85 cents/kWh, from WVIC. The data collected by the National Power Association shows that hydropower has a relatively low cost compared to all the other renewable sources, in terms of maintenance, operations, and fuel costs. IRENA states that the average investment costs for large hydroelectric power plants are around $1,050/kW to $7,650/kW and smaller hydroelectric power plants range from $1,300/kW to $8,000/kW. Although at first glance, it may seem expensive, it is spread across a long timeframe and the fact that it doesn’t require major replacements or repairs. Furthermore, once the equipment for the hydroelectric power plant is constructed, there are no combustion emissions, no fuel costs, and very low operating and maintenance costs. They can be easily upgraded when new and recent technology is developed, (Perlman, 2016). Not only is hydropower inexpensive, it is also a very efficient way to generate electricity. According to WVIC, modern hydro turbines can convert as much as 90% of the available energy into electricity whereas the best fossil fuels plants are only about 50% efficient. Moreover, in the hydroelectric power plant system, water is not modified and can be used to produce more electricity, (Thygesen, 2014). Compared to fossil fuels and nuclear energy, hydroelectricity is considered to be a much safer environmental choice as there is no fuel that creates pollution, (Maehlum, 2014). Hydropower is clean and renewable because it doesn’t pollute the air or the water and that fuels are not burned to emit greenhouse gases. It uses the Earth’s water cycle to generate electricity; the sun causes the water to evaporate from the Earth’s surface to form clouds that fall back to Earth in the form of rain or snow, (Maehlum, 2014) and the cycle repeats. This keeps the hydroelectric power plant supplied with water, with the ability to generate electricity. However, to build the hydroelectric power plant, it takes carbon-based energy, which produces pollution. According to the Régie de l’énergie, it takes 4 to 7 years to build a hydroelectric power plant. The USGS Water Science School states that hydroelectric power plants last around 50-100 years. The 50-100 years that is free of pollution and greenhouse gases make up for the 4-7 years that creates pollution. The purpose of hydroelectric power plants is to generate electricity without emitting large amounts of greenhouse gases, like power plants that burn fossil fuels. Power plants that burn fossil fuels create pollution and emit greenhouse gases when making the plant as well as the usage of it. However, hydroelectric power plants create pollution when making it, but does not emit after building the power plant. There are some harmful effects from creating hydroelectric power plants, such as the disruption to the aquatic ecosystem. When fish swim under a gate from a dam, the pressure of water increases with depth and the velocity often exceeds the speed at which fish can keep control of their own swimming which throws them to objects, walls, or other fish, (Conca, 2014). It also prevents migrating fish, such as salmon, from crossing the hydroelectric dam. Some dams, such as the Bonneville Dam, have installed fish ladders to help fish migrate, (National Geographic, 2011). Fish ladders are a series of wide steps built on the side of the river and dam. The ladder allows fish to slowly swim upstream instead of being blocked by the dam. Fish ladders can be installed in most hydroelectric dams to allow fish to migrate. In conclusion, it is justified to use carbon-based energy to produce low-carbon energy because of the advantages and the cost factor that hydroelectric power plants have. Not only that but the fact that hydropower is very efficient and that it does not produce a large number of greenhouse gases. Even though it has some disadvantages, there have been possible ways to solve the situation.