A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aquaculture, and navigability. Hydropower is often used in conjunction with dams to generate electricity. A dam can also be used to collect or store water which can be evenly distributed between locations. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees (also known as dikes) are used to manage or prevent water flow into specific land regions. The earliest known dam is the Jawa Dam in Jordan, dating to 3,000 BC.

Glen Canyon Dam on the Colorado River, Arizona, USA
Lake Vyrnwy Dam, Wales, finished in 1888
Karapuzha Dam, an earthen dam in the Indian state of Kerala
Small dam near Groningen, Netherlands

The word dam can be traced back to Middle English,[1] and before that, from Middle Dutch, as seen in the names of many old cities,[2] such as Amsterdam and Rotterdam.

Afsluitdijk with the Wadden Sea (a part of the North Sea) on the left and the IJsselmeer on the right in the Netherlands