Hydro Power

Instead of using steam to drive generator turbines, a hydro plant uses the force of falling or flowing water.
Hydro power has been used to make electricity in the Midwest since the early 1900s, with many facilities built by the Works Progress Administration in the 1930s.
There are two types of hydroelectric power plants:

• A high-head plant takes advantage of the force of falling water. Large-scale facilities like the Hoover Dam and Grand Coulee Dam are examples of high-head hydro plants. Dams are built along major rivers to create reservoirs; the utility controls the flow of water through the dam in response to the demand for electricity.
• A run of the river plant, like those found in the Midwest, relies on the flow of the river to spin the turbines. These plants produce a much smaller amount of electricity.
  The benefits of hydro power are many: no hazardous emissions or solid waste, no fuel costs and it's entirely sustainable. Hydro plants are reliable, low maintenance and provide flood control.
  

Drawbacks to hydro power :

• Environmental groups have pointed out the drawbacks to hydroelectric power, especially from large-scale dams and reservoirs. The most dramatic is the impact on wildlife - the reservoirs can alter water temperature and prevent the migration of fish.
  
• While "run of the river" hydro plants have a much smaller environmental impact, their use is constrained by the lack of control. The electricity produced at these plants cannot be increased or decreased according to demand, and the flow of the river is dependent on the area's precipitation.
  
• Many of the nation's hydroelectric plants are aging, and flooding in recent years has irreparably damaged several in the Midwest. The initial costs of building or replacing a hydro plant are high, and usually not cost-effective in the Midwest, so most utilities are investing in other forms of renewable energy.