What are the advantages and disadvantages of using hydroelectric energy?

What are the advantages and disadvantages of using hydroelectric energy?

- Hydropower can be used to generate either electrical power or mechanical power to run machinery; its use may help reduce the high cost of importing energy

- Can help small operations become more independent of local utility providers.

- Water power is clean power; it requires no burning of fuel, does not pollute the atmosphere, produces no radioactive or other waste, and is efficient.

Environmental prices to pay ( Disadvantages of using hydroelectric energy) :

• Large dams and reservoirs flood large tracts of land that could have had other uses - towns and agricultural lands may be lost.
• Dams block the migration of some fish.
• Dams trap sediment that would otherwise reach the sea and eventually replenish the sand on the beaches.
• Many people do not want to turn wild rivers into a series of lakes.
• Reservoirs with large surface areas increase evaporation of water compared to pre-dam conditions. In arid regions, this could have a bigger impact. 
• Water falling over high dams may pick up nitrogen gas; if the gas enters the blood of fish, it expands and kills them.