Overall hydro power safe than fossil fuel systems and nuclear as the are are no site air emissions, no waste and no thermal degradation of water.
The creation of hydro power usually requires the diversion of the water at an existing waterfall or the creation of a reservoir. The diversion of a waterfall may not cause problems as the water is eventually released to the same water course. The hydro power reservoir with its associated dams is another case. These systems can:
- be an impediment for spawning fish
- flood ecosystems
- result in methane losses from decomposing drowned vegetation
- change the hydrodynamics of the lower reaches of rivers