What are the main purposes and benefits of dams?

Dam is a specific structure built across a stream, a river, or an estuary to retain water. Dams are built to provide drinking water for human consumption, for irrigating arid and semiarid lands, or for use in industrial processes. They can also be used to generate electricity as hydropower plants, to reduce peak discharge of floods created by large storms or heavy snowmelt, or to increase the depth of water in rivers to improve ship transportation. The upside is that dams can also provide a lake for recreational activities such as swimming, boating or fishing. Many dams are built for more than one purpose; for example, water in a single reservoir can be used for fishing, to generate hydroelectric power, and to support an irrigation system and as a protection from floods. Water-control structures of this type are often designated as multipurpose dams.