A dam's a barrier that impounds water or underground streams. 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. Hydropower and pumped-storage hydroelectricity are often used in conjunction with dams to provide clean electricity for millions of consumers. History The word dam can be traced back to Middle English, and before that, from Middle Du… (More on Dam)