In a world in search of “green” energy, hydropower is often proposed as an environmentally positive option. According to the industry’s sup-porters, dams do not produce emissions that might exacerbate the green-house problem, acid rain or urban sm og—ineluctable consequences of using fossil fuels. Nor do they generate volumes of waste that create a range of harms for future generations. And, unlike natural gas, the future of hydropow er is secure. A ccording to the National Hydropow er A ssociation, the trade association representing U.S. hy-dropow er interests (www.hydro.org):

Hydropower is an emissions-free, renewable and reliable energy source that serves our national environmental and energy policy objectives. With zero air-emissions, hydropower helps in the fight for cleaner air. Hydropower’s fuel—water—is essentially infinite and is not depleted in the production of energy. This helps to preserve our nation’s independence from supply disruptions overseas. And, as a source of energy, hydropower excels at preserving the stability and reliability of the electrical grid due to its unique operating characteristics.