The correct answer is: All of the above.
Large dams have a number of negative impacts on the environment and people. They can displace communities, disrupt ecosystems, and impact downstream water flow.
Displacement of communities: Large dams often require the relocation of entire communities. This can be a very disruptive process, as people are forced to leave their homes and livelihoods. In some cases, communities have been displaced multiple times due to the construction of multiple dams.
Environmental impacts: Large dams can have a number of negative impacts on the environment. They can alter the flow of rivers, which can impact fish populations and other aquatic life. Dams can also lead to the loss of wetlands and other important ecosystems.
Downstream water flow: Large dams can also impact downstream water flow. This can lead to water shortages for downstream communities, as well as changes in the water quality. In some cases, dams have even led to the extinction of fish species.
In addition to these negative impacts, large dams are also often very expensive to build and maintain. They can also be a source of conflict between different groups of people. For all of these reasons, large dams are often controversial projects.