What is a disadvantage of using moving water to produce electricity

Most of the time the towns get flooded and many people die and lose their homes and their jobs, businesses by the floods and the natural environment is destroyed ,air pollution is produced, the ecosystem could be disrupted and dams are known to fall over and dams are really expensive to build, The dams also cause geological damage, example earthquakes and spills happen.

The independent variable would be the fertilizer as it is what the dependent variable (the growth of grass) depends on.