A dam is a barrier or structure across a stream, river, or waterway to hold back and then control the flow of water. Dams vary in size and type from small earthen embankments to high concrete structures. They serve a diverse set of functions, ranging from flood protection, water storage, and hydroelectric power to irrigation, farm ponds for livestock, and recreation.
In this report, we describe dams in the United States, including where they are located, their age and size, who owns them, and what primary purpose they serve. We also describe their hazard ratings, which provide a measure of the potential damages resulting from dam failure, and condition assessments, which give some information about the physical condition of a dam (and thus its likelihood of failure).
As with much infrastructure in the United States, many dams are aging and in need of repair. For many of these aging and failing dams, especially those that no longer serve a valuable function, removal might be the best option. We provide summary data about the dams that have been removed in the United States through 2019.
This report is a companion study to five other Resources for the Future reports and issue briefs on dams and dam removals, which include a cross-state comparison and analysis of dam safety regulations and policies and their alignment with dam removal and four issue briefs on funding options for dam removal.