Hydropower harnesses the energy of moving water and has been used for over 2000 years to grind wheat and power factories. In the late 1800s, hydropower began to be used to generate electricity. Dams create reservoirs that store the potential energy of water, which is then released to spin turbine blades and generate electricity in power plants without pollution. While hydropower is a renewable energy source, dams can flood land and disrupt wildlife habitats.

3. Photograph of old power plant above Niagara Falls

4. Niagara Falls , American Falls

5. Easier to build on a river where there is a natural waterfall Athabasca Falls, Oregon

6. Dams make artificial waterfalls Bonneville Dam on the Columbia River between Washington & Oregon

7. The water held back by the dams (reservoirs) are stored energy Lake Powell Utah

8. The dam needs gates to open & close

11. Old turbine being removed

14. Replacement Turbine

15. the generator (the turbine is underneath)

18. Power plant at Bonneville Dam

21. Example: Pacific Salmon

26. Top view of fish ladders

29. Window into fish ladder

35. http://www.msnbc.msn.com/id/21134540/vp/24253799#24253799