Environmental Impact

While hydropower does not cause water or air pollution, it does have an environmental impact. Hydroelectric power plants may harm fish populations, change water temperature and flow (disturbing plants and animals) and force the relocation of people and animals who live near the dam site.

Some fish, like salmon, may be prevented from swimming upstream to spawn. Technologies like fish ladders help salmon go up over dams and enter upstream spawning areas, but the presence of hydroelectric dams changes their migration patterns and hurts fish populations. Hydropower plants can also cause low dissolved oxygen levels in the water, which is harmful to river habitats.

A dam that creates a reservoir (or a dam that diverts water to a run-of-river hydropower plant) can change natural water temperatures, water chemistry, river flow characteristics and silt loads. All of these changes can affect the ecology and the physical characteristics of the river. These changes may have negative effects on native plants and on animals in and around the river. Reservoirs may cover important natural areas, agricultural land or archeological sites. A reservoir and the operation of the dam may also result in the relocation of people. The physical impacts of a dam and reservoir, the operation of the dam and the use of the water can change the environment over a much larger area than the area a reservoir covers.Reservoirs may also lead to the creation of methane, a harmful greenhouse gas.



Pros and cons of hydropower as an energy source

No emissions
Capable of generating large amounts of power
Output can be regulated to meet demand
Low maintenance and silent
Environmental impacts in the dam construction area
Expensive to build
Dams may be affected by drought
Carbon dioxide and methane emissions
Risk of flood in lower areas