Dam

A dam is a large wall or barrier that blocks or stops the flow of water, forming a reservoir or a lake.^[1] Most dams have a section called a spillway or weir over which, or through which, water flows, either sometimes or always. Dams generally serve the primary purpose of retaining water. The tallest dam in the world is the 300 meter high Nurek Dam in Tajikistan.

1. ↑ The American Heritage Dictionary of the English Language, Fourth Edition