Hydro-electric power is classified among Renewable Energy Sources where no contributions to man-made global warming. But what how friendly is hydro-electric power? and what are the environmental threats associated with this source of energy?. So far, our accumulated knowledge demonstrates that the environmental threats were under-estimated. The hydropower seems to be viewed more favorably, despite historical concerns over biodiversity loss, long-term environmental impact and the social repercussions of massive community resettlement. Natural erossion at upstream lands that deliver fertile soils to low laying-land downstream has long-term impacts on soil quality with consequences for continuous use of fertilization, e.g. the case of the Nile delta. Inceasing of evaporation at the water-bodies behind dam constructions which is dominant in arid and regions, e.g. Lake Naser on the Nile. Dam building is expected to give rise to changes in local and regional hydrology of groundwater with risks for increasing salination, if this takes place in combination with increased use of groundwater. Also, power plants at upstream countries are usually associated with increasing waste and pollution from the industries, urbanization activities and household. Such emissions in many cases do not follow strict environmental protection recoomendations.

See more at:
http://chinawaterrisk.org/resources/analysis-reviews/hydropower-environmental-disaster-or-climate-saver/