1) Disrupts aquatic ecosystems: The dams developed across the rivers can disturb aquatic life and lead to their large scale destruction. There is a chance that fish and other water animals may enter the penstock and ultimately the power generation turbines where they will be killed. Dams can also disturb the mating seasons and mating areas of the water animals.
In some cases water animals have to swim against the water stream during breeding seasons. If a dam is built in the path of migrating fish they could be stuck there and killed, never reaching their destination. This could devistate a population of fish.
2) Disruption in the surrounding areas: Plant and animal life around rivers thrive due to continuous fresh flowing water in the river. Due to construction of the dams lots of areas have to be cleared that disrupt the plant and animal life. In many cases even a number of trees have to be cut that destroys not only the plant life but also the animals dependent on them. Even changing the course of flow of water in the river due to the construction of the dam disrupts the plants and animals life.
3) Requires large areas: In order to build a dam, power generation unit and transformers, and connect them to the national grid, a huge amount of land is needed. This requires forests to be cleared disrupting many local, natural ecosystems.
4) Large scale human displacement: Because these dams take up such a large area, it is often necessary for humans to relocate. It is not easy to convince people to uproot their lives and businesses. Often they are not compensated fairly for their land and the inconvenience. This creates large scale opposition and revolts against construction of the dams.
In India we have seen a large opposition to the one of the biggest hydroelectric power projects named “Sardar Sarovar." Though millions of people are to benefit from the project, government didn’t manage the important issue of the resettlement of people who were displaced from the adjoining areas of project. This led to one of biggest protests in Indian history, which saw a number of hunger strikes, protest marches and even police attacks on the protesters.
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