Question

why is construction of dams considered a threat to our enviroment?

Answer 1

because due to the construction of dams aquatic life get affected, mainly during its migration. Also by this sediment flow through river is affected.

Answer 2

Flooding and the destruction of surrounding habitat: Dammed rivers create a reservoir upstream from the dam, which spills out into the surrounding environments and floods ecosystems and habitats that once existed there. Such flooding can kill or displace many different organisms, including plants, wildlife, and humans.