Two primary disadvantages of hydroelectric power include the high investment cost and its reliance on precipitation. Hydropower facilities can have a negative impact on the environment, despite not causing pollution, including the loss of fish habitats, displacement of the local population and the inundation of surrounding land.
A hydroelectric power plant requires a water reservoir, the size of which depends on the size of hydroelectric generators and the topography of the land. Creating a reservoir negatively impacts the surrounding area by flooding land that could be used for agriculture instead. Furthermore, it has a damaging effect on the surrounding wildlife due to the power plant causing a change in the water temperature and modifying the river flow. Some reservoirs can lead to a buildup of methane that subsequently releases into the atmosphere.
Reservoirs also affect the quality of the water downstream of the facility. The water is more stagnant than normal, which leads to increased levels of sediment and nutrients that benefit the growth of algae and other aquatic weeds. If operators fail to periodically release enough water from the reservoir, the downstream water levels can drop significantly, endangering animal and plant life.
The use of hydroelectric power also carries the risk of a dam failure, which can have a catastrophic effect on downstream settlements and infrastructure.