A dam is a structure built to impound water in a river or stream, creating a reservoir for various purposes such as irrigation, flood control, and hydroelectric power generation. Dams are typically constructed using materials like concrete or earth, and can vary in size from small barriers to large structures spanning across a river valley.

The construction of dams has both positive and negative impacts on the environment and surrounding communities. While dams provide important benefits like water supply and renewable energy, they can also disrupt ecosystems, alter natural water flow patterns, and displace communities. Proper planning and management are crucial to ensure that dams are built and operated in a sustainable manner that minimizes their negative effects.