During the early part of the 20th century, America's rivers became dammed at a prodigious rate. Virtually every major American river is dammed at multiple points. Virtually every dam is silting rapidly behind the dam, as the normal sediment flow is interrupted.
All dams are temporary, geologically-speaking. And our nation's dams, like so much of our infrastructure, are not holding up well.
As this recent report in the New York Times details, if you have water flowing out of your tap, you live downstream from a dam. You might not be directly in the flow expected from a dam failure, but many of your neighbors are.