Dams & river regulation have become an integral part of 20th-century landscape & livelihood. Virtually every river in the lower 48 states is now regulated by dams, locks, or diversions. This report illustrates the downstream consequences of dams & explains the basis on which rivers can be scientifically managed. Following a look at a free-flowing river -- the upper Salt River of Arizona -- & its natural cycles of flow & sediment, 6 regulated rivers are examined. Each of these rivers -- the Snake, Rio Grande, Chattahoochee, Platte, Green & Colorado -- highlights a particular use of a dam or a particular downstream effect.