A dam (a common Teutonic word, compare to Dutch dam, Swedish and German damm, and the Gothic verb faurdammjan, to block up) is a barrier across flowing water that obstructs, directs or retards the flow, often creating a reservoir, lake or impoundment. Most dams have a section called a spillway, over which or through which it is intended that water will flow.
Dams may be classified according to structure, intended purpose or height.
Based on structure and material used dams are timber dams, embankment dams or masonry dams (arch or gravity type).
Intended purposes include providing water for irrigation or town or city water supply, improving navigation, generating hydroelectric power, creating recreation areas or habitat for fish and wildlife, flood control and containing effluent from industrial sites such as mines or factories. Few dams serve all of these purposes but some multi-purpose dams serve more than one.