Dam

A dam is a barrier across flowing water that obstructs, directs or slows down the flow, often creating a reservoir, lake or impoundment. In Australian and South African English, the word "dam" can also refer to the reservoir as well as the structure. Most dams have a section called a spillway or weir over which, or through which, water flows, either intermittently or continuously.

Dams generally serve the primary purpose of retaining water, while other structures such as levees and dikes are used to prevent water flow into specific land regions.