While damming a river can provide a large population with a reliable source of drinking water and an environmentally friendly source of electricity, it often has several negative consequences for the population in the vicinity of the dam:
- The lake which will form on the upstream side of the dam might swallow privately owned lands, privately owned homes or even whole villages. For example, this picture from Lake Reschen in Italy shows you a church tower (European equivalent of a minaret) in the middle of a lake. It used to belong to a village which used to be home of several hundred people until a dam was built in the 1940s.
- The downstream water system will be affected, which might lead to farmland which used to be fertile to become arid and might make fishing impossible where it used to be possible. Local farmers and fishers might fear for their existence.
- If the river used to be suitable for ships, it likely won't be after the dam is built. This destroys local infrastructure and might have negative economic consequences.
- Environmental concerns about the destruction of natural ecosystems.
This makes dam construction projects examples of Not-In-My-Backyard issues. Of course everyone wants clean water and clean energy for the country, but nobody wants their personal life destroyed because of it. So a vocal local minority will be willing to do anything to prevent such a project from being completed.
Why can't the Army take control on construction of the Dam?
Be careful what you wish for. Using the army to solve internal problems with force often leads to an escalation of conflicts which can lead to all out civil wars. Extending the responsibilities of the army to areas which are not their primary duty (defending the country against external aggressors) is creating a dangerous precedent which might lead to the army taking control of even more civil tasks and can end in a military dictatorship.
There is a reason why the most economically successful countries in the world solve such conflicts in a democratic manner. Talking things out and coming to compromises might be less efficient, but it leads to far fewer people getting imprisoned or shot.