Mitigation measures such as fish ladders that protect spawning and the choice of a hydro facility's location are critical features. Hydropower currently provides about 10 percent of the electricity generated in the United States - a percentage unlikely to increase dramatically, both because few new sites remain for the construction of large dams and because of general opposition to building large new facilities on environmental grounds. These plants are very efficient and only produce a fraction of the air pollution of other types of fossil-fuel fired power plants. Some people may believe that by specifying their preference for Green Power they will get power exclusively from renewable sources. To understand this concept, think of your local electricity grid as a reservoir, river or lake with many sources.
Power generators pour energy into the reservoir and customers draw it out.
In this way, decisions to purchase Green Power change the overall mix of electricity being generated and encourage more investment in renewables. Green Regulation State and federal governments are considering a variety of policy measures to respond to the public concerns over the potentially adverse effects that electricity restructuring may have on the environment. Most policies are incentives or regulations that encourage the use of renewables. They differ from place to place and have so far had varying degrees of success. Performance-based regulations , which may be used to target profits to renewable usage or through placing limits on pollutant emissions.