The environmental impacts of hydropower

While hydropower is clean and renewable, there are unique environmental side effects to the technology. The environmental impact of hydroelectric generation is complicated and necessitates examining the lifecycle of a hydropower plant. As new and improved hydropower technologies continue to be developed, hydroelectricity has the chance to become an even cleaner source of power.

First and foremost, hydropower is a source of clean and renewable electricity. No fossil fuels need to be burned to generate hydroelectricity, and the water cycle is constantly running naturally, meaning we won't run out of hydropower. Hydroelectric generation isn't limitless, however, as there is a finite amount of water on Earth available to be harnessed (especially considering how many rivers have already been dammed).

Hydroelectricity is technically a "clean" energy source, but there are environmental ramifications of harnessing it for large amounts of power. Here are a few of the consequences that come with developing hydropower systems:

Damage to wildlife habitats and migratory paths

Constructing large storage or pumped storage hydropower plants involves blocking, diverting, or changing the natural course of river systems. 

One issue that arises with blocking a river's natural flow is the simultaneous blocking of important migration routes for fish. Many species of fish depend on inland rivers for reproduction; by blocking a river's flow with dams, fish cannot reach their breeding grounds. Over time, dammed rivers lead to drastically reduced fish populations, which has negative implications for the health of river ecosystems as well as for human food stocks. Some hydropower facilities use fish ladders to help fish populations traverse dammed rivers, but these devices are rarely large enough to support massive migrations.

Additionally, damming rivers also often reduces water and sediment flow to dangerous levels, which impacts downstream wildlife populations. Low water flow downstream, as well as low nutrient flow, can lead to loss of habitat and healthy water for animals.

Land use

On a similar note, many large hydropower facilities alter the surrounding landscape, especially around reservoirs created by damming rivers. Just as reducing downstream water flow can cause habitat loss, creating reservoirs to generate electricity in storage and pumped storage hydropower systems often cause upstream flooding that destroys wildlife habitats, scenic areas, and prime farming land. In some instances, this flooding can even force human populations to relocate.

Greenhouse gas emissions from reservoirs

While generating power by spinning turbines with water doesn't directly use any fossil fuels or emit greenhouse gases, several recent studies have shown that reservoirs created by damming rivers contribute significantly to atmospheric greenhouse gases. This is because organic material trapped in the reservoirs, such as dead plants, breaks down and releases gases like carbon dioxide and methane into the reservoir water.

Fortunately, there are ways to improve hydropower systems to be more environmentally friendly. One such strategy is to better plan land use around river basins upstream of dams. By protecting the natural environment in a river's watershed, erosion can be better contained, which can help lessen greenhouse gas pollution into the air from reservoirs, as there will be less decaying organic material in the water.

Progress is also being made to reduce hydropower's impact on fish habitats and migrations. Some hydroelectric facilities use trap-and-haul programs to collect fish, transport them past a dam, and release them. The Department of Energy (DOE) has recently even sponsored research and development of "salmon cannons," which launch migrating fish over a dam. A more sustainable long-term solution for many locations is more careful planning of dam placement so that the most important migration paths aren't disturbed. In some cases, removing old dams and letting the river flow return closer to its natural state leads to habitat restoration for fish species.

Additionally, newer ways to harness power from water continue to be developed, such as tidal power and wave energy, which tend to have a smaller environmental footprint than traditional storage hydropower systems.