The term hydroelectric is used to describe the generation of electic power through the natural flow of water.
The earliest hydroelectric projects were erected in the late 19th Century. They were often erected with little or no regard to the environmental impact of the dams necessary to provide a "head" of water. Dams can disrupt the migration of fish species, like Salmon, and can disrupt the flow of silt from the river's upper reaches. Notably, this was one of the unintended consequences of the Aswan High Dam, in Egypt.