Laurie Campbell / Outfall from hydroelectric Laggan Dam, Lochaber, Scotland, UK, February

Norbert Wu / Glen Canyon Dam on the Colorado River which generates hydroelectric power and the Glen Canyon Bridge, Glen Canyon National Recreation Area, Arizona

Luiz Claudio Marigo / Canyon of Sao Francisco River near Paulo Afonso town and the CHESF hydroelectric plant and dam, in northeastern Bahia State, northeastern Brazil. December 2009

Jerry Monkman / Comerford Dam and hydroelectric power station on the Connecticut River in Monroe, New Hampshire, USA. April 2007

James Christensen / John Day Dam, Columbia River, Oregon

Laurie Campbell / Outfall from hydroelectric Laggan Dam, Lochaber, Scotland, UK, February

Laurie Campbell / Outfall from hydroelectric Laggan Dam, Lochaber, Scotland, UK, February

Laurie Campbell / Outfall from hydroelectric Laggan Dam, Lochaber, Scotland, UK, February

Luciano Candisani / Itaipu Dam, the largest in the world, Parana River near Iguacu Waterfalls, Brazil

Luciano Candisani / Machadinho Dam, small hydroelectic plant in Parana River, Brazil

Norbert Wu / Glen Canyon Dam on the Colorado River which generates hydroelectric power and the Glen Canyon Bridge, Glen Canyon National Recreation Area, Arizona

James Christensen / John Day Dam, Columbia River, Oregon