How do hydroelectric dams affect the environment?
They destroy the local habitat and environment, reduce the flow of the river downstream
For a hydroelectric dam to produce a controlled amount of electricity, it needs to have a reservoir. The reservoir directly destroys the local environment by flooding it and raising the water table.
The dams also reduce the flow of the river downstream in order to control the amount of electricity being produced. Thus the smaller flow may be harmful for some organisms that require deep, flowing water, such as the Yangtze river dolphin.