Hydraulic energy is what is produced by the water which is stored in  reservoirs and lakes at a high altitude (so that it has gravitational potential energy). If at a given moment it falls to a lower level, this energy is transformed into kinetic energy and afterwards into electrical energy in the hydroelectric plant.

Advantages: it is a clean energy source, without waste products and is easy to store. Also the water stored in reservoirs situated at altitude permits the regulation of the flow of the river.

Disadvantages: the construction of hydroelectric plants is expensive and needs  large  networks of power cables. Reservoirs also mean the loss of productive soil and fauna due to the flooding of their habitat. They also cause a decrease in the  flow of the rivers and streams below the dam and alter the quality of the waters. The following animation shows how hydraulic energy is stored and exploited.