Advantages of Hydropower:
Hydro power is a very efficient source of renewable energy. Because of the density of water and the force of gravity (among other factors) the hydropower technological advantages of today are that these systems can covert up to 90% of the energy of water into electric energy, which is an astonishing number.
Because of this efficiency the cost of hydroelectricity has dropped with evolving technologies, and is estimated to be about 40% less expensive than using fossil fuels.
Since hydro power is fueled by water, it has the advantage of being only used when needed, because it is easy to control the storage and allowable flow of water into a hydro power system.
Hydro power has an advantage over wind power because water is more dense than air, so collecting the mechanical energy of wind requires a greater force of wind to rotate the turbine than it would for water in a hydro power system.
Disadvantages of Hydropower:
A big disadvantage of hydropower is the negative impacts that a large-scale dam and reservoir hydro system has on the environment. (Impact of hydropower on the environment)
Hydropower is, like other sources of renewable energy, very expensive to implement, so it takes a long amount of time before a hydropower system will begin to return profits on the original cost of the investment.