At one point, the Ross Dam near Seattle was considering a major expansion which would have flooded millions of acres of land, but the project was halted because of environmental and political concerns. Damming a river and creating a lake environment results in dramatic changes in the timing of flow, quality, quantity, and use of water, aquatic biota, and sedimentation dynamics in the river basin. Hydroelectric plants create major changes in the river flow patterns downstream because storage and realeases are managed in response to power demand cycles rather than the hydrological cycles. Fish and wildlife need to be conserved and enhanced. Wetlands need to be preserved.
Reservoirs can cover towns, scenic locations and farmland.