The impacts caused by construction of dams and reservoirs include

The impacts caused by construction of dams and reservoirs include Soil erosion, Loss of vegetation cover and Change in microclimate.
The environmental impact of reservoirs comes under ever-increasing scrutiny as the global demand for water and energy increases and the number and size of reservoirs increases.
The construction of a dam blocks the flow of sediment downstream, leading to downstream erosion of these sedimentary depositional environments, and increased sediment build-up in the reservoir.
Reservoirs may contribute to changes in the Earth's climate. Warm climate reservoirs generate methane, a greenhouse gas when the reservoirs are stratified, in which the bottom layers are anoxic, leading to degradation of biomass through anaerobic processes.