National Geographic's Dams Web site offers an interactive investigation into the good and bad impacts of dam construction. Visitors choose to view a river system before, during, or after a dam is built. Then at each time interval they can click on various sections of the river and read a short description of what is happening there. For example, after the dam is built, the reservoir that is created upstream causes several hydrological problems such as loss of water from evaporation. Although the text provided on the site is somewhat lacking, the well-done graphics and interactivity make it worth a visit.