High investment costs
Dependent on precipitation
Sometimes messes up wildlife
Loss of fish species
Change in river or stream quality
Cost for construction
Hydroelectric power production require flooding of entire valleys and scenic areas.
Disrupts natural seasonal changes in he river, and ecosystems can be destroyed.
Ends flooding that help to clean out the silt in rivers, causing them to clog (Energy Laboratory).
The silt that usually flows down to the Beaches and Estuaries is block by the dam.
Studies show that the plant decay caused downstream of major dams produces as many greenhouse gasses as more conventional methods of producing electricity.
Dams are expensive to build, and due to drought may become useless, or produce much less power than originally planned.
A dam being build in Quebec will end up flooding an area as large as Switzerland (Energy Laboratory).
Dams can break in a massive flash flood
Construction costs of large-scale hydroelectric projects are high.
Damming rivers causes changes in ecological cycles and surrounding landscapes; self-regulating ecosystems are changed into ones that must be managed.
Sedimentation can progressively curtail a dam's ability to store water and generate energy.
There are a limited number of feasible sites for large dams.
Damming can cause loss of land suitable for agriculture and recreation.
Drought can affect power production.
Dams are vulnerable to natural forces. There is a high direct death rate from the failure of dams.
River channels downstream from dams are more susceptible to erosion.
A disadvantage of hydroelectric power stations is that it destroys wildlife and habitats of any creatures living in the area.
Dams are extremely expensive to build and must be built to a very high standard.
The high cost of dam construction means that they must operate for many decades to become profitable.
The flooding of large areas of land means that the natural environment is destroyed.
People living in villages and towns that are in the valley to be flooded, must move out. This means that they lose their farms and businesses. In some countries, people are forcibly removed so that hydro-power schemes can go ahead.
The building of large dams can cause serious geological damage. For example, the building of the Hoover Dam in the USA triggered a number of earth quakes and has depressed the earth's surface at its location.
Although modern planning and design of dams is good, in the past old dams have been known to be breached (the dam gives under the weight of water in the lake). This has led to deaths and flooding.
Dams built blocking the progress of a river in one country usually means that the water supply from the same river in the following country is out of their control. This can lead to serious problems between neighboring countries.
Building a large dam alters the natural water table level. For example, the building of the Aswan Dam in Egypt has altered the level of the water table. This is slowly leading to damage of many of its ancient monuments as salts and destructive minerals are deposited in the stone work from 'rising damp' caused by the changing water table level.
Hydro power dams can damage the surrounding environment and alter the quality of the water by creating low dissolved oxygen levels, which impacts fish and the surrounding ecosystems. They also take up a great deal of space and can impose on animal, plant, and even human environments.
Fish populations can be impacted if fish cannot migrate upstream past impoundment dams to spawning grounds or if they cannot migrate downstream to the ocean. Upstream fish passage can be aided using fish ladders or elevators, or by trapping and hauling the fish upstream by truck. Downstream fish passage is aided by diverting fish from turbine intakes using screens or racks or even underwater lights and sounds, and by maintaining a minimum spill flow past the turbine.
Hydro power can impact water quality and flow. Hydro power plants can cause low dissolved oxygen levels in the water, a problem that is harmful to riparian (riverbank) habitats and is addressed using various aeration techniques, which oxygenate the water. Maintaining minimum flows of water downstream of a hydro power installation is also critical for the survival of riparian habitats.
Hydro power plants can be impacted by drought. When water is not available, the hydro power plants can't produce electricity.
New hydro power facilities impact the local environment and may compete with other uses for the land. Those alternative uses may be more highly valued than electricity generation. Humans, flora, and fauna may lose their natural habitat. Local cultures and historical sites may be flooded. Some older hydro power facilities may have historic value, so renovations of these facilities must also be sensitive to such preservation concerns and to impacts on plant and animal life.
By 2020, it is projected that the percentage of power obtained from hydro power dams will decrease to around four percent because no new plants are in the works, and because more money is being invested in other alternative energy sources such as solar power and wind power.
Dams usually flood large river valleys, covering a lot of native habitat with water, displacing animals and sometimes people. In China more than one million people were moved when they built their big "Three Gorges" dam. Many archaeological sites are now unreachable under water and there is environmental damage along the banks of the many tributaries of the Yangtze Rive