The electricity generated from the energy of flowing water or fast-moving water is known as hydropower or hydroelectricity. This is considered a renewable source of energy because the water cycle is constantly renewed by the sun. The most common type of hydropower plant uses a dam on a river to store water in the reservoir. Released water from the reservoir flows through a turbine, spinning the turbine, which in turn activates a generator to produce electricity. But hydropower always does not require large dams. Few power plants use a mini version of canals to connect the river water with the help of turbines. Another kind of hydropower plant, pumped storage plant is used to store power. The energy is transmitted from a power grid into the electric generators. After that, the generators spin the turbines in the backward direction, which causes to pump the water from a river or lower reservoir to an upper reservoir, where the power is stored. After that, the water is released from the upper reservoir back to the lower reservoir or river and that flow spins the turbines forward, starting the generators to generate electricity. A small or micro-hydroelectric power system can produce enough electricity for a home, farm or ranch. Hydropower contributes to 10% of world electricity generation. Although there is no air emission, however, water quality and wildlife habitats can be affected. Work is going on to design the power plants in such a way that it causes the minimum effect on the river water. Undoubtedly it improves the wildlife’s river habitat but at the same time cause the reduction in power plant output. Sometimes this power plant hinders the life of the fishes so different approaches are employed such as fish ladders and improved turbines to assist the migration of fishes and lower their death rate.