Concrete dams are large structures built across rivers or streams to hold back water. They are made primarily of concrete, which provides strength and durability. These dams create reservoirs that can store water for various uses, such as drinking, irrigation, and hydroelectric power generation. The design of concrete dams often includes a curved shape, which helps distribute the water pressure evenly. This type of dam is commonly used in many countries due to its effectiveness and longevity. Notable examples include the Hoover Dam in the United States and the Aswan High Dam in Egypt.