The main environmental impact of development projects like large dams and reservoirs is extensive deforestation.

Deforestation:
Large dams and reservoirs require vast amounts of land for construction. This often involves clearing large areas of forests to make way for the project. The removal of trees and vegetation leads to deforestation, which has several negative consequences for the environment.

Loss of Biodiversity:
Deforestation caused by the construction of large dams and reservoirs results in the loss of habitat for numerous plant and animal species. Forests are incredibly diverse ecosystems, home to a wide range of flora and fauna. When forests are cleared, many species lose their homes and are unable to survive. This loss of biodiversity can have far-reaching ecological consequences.

Disruption of Ecosystems:
Forests play a crucial role in maintaining ecological balance. They help regulate temperature, provide oxygen, absorb carbon dioxide, and contribute to the water cycle. Deforestation disrupts these important ecosystem services, leading to imbalances and negative impacts on the environment.

Soil Erosion:
One of the direct consequences of deforestation is soil erosion. The removal of trees and vegetation leaves the soil exposed to erosion by wind and water. Without tree roots to hold the soil in place, it can easily be washed away or blown away. This erosion degrades soil quality and can lead to decreased agricultural productivity in the long term.

Loss of Carbon Sink:
Forests act as carbon sinks, absorbing carbon dioxide from the atmosphere and storing it in trees and soil. When forests are cleared, this carbon is released back into the atmosphere, contributing to greenhouse gas emissions and climate change.

Conclusion:
While development projects like large dams and reservoirs can bring economic benefits and meet the growing energy and water demands of a population, it is important to consider the environmental impacts. Extensive deforestation caused by these projects has significant negative consequences for biodiversity, ecosystems, soil quality, and climate change. Therefore, it is essential to implement sustainable practices and mitigate the environmental impacts associated with such development projects.