The environmental impact of reservoirs comes under ever increasing scrutiny as the global demand for H2O and energy increases and the number and size of reservoirs increases. Dams and reservoirs can be used to supply drinking water, generate hydroelectric power, increase the water supply for irrigation, provide recreational opportunities, and improve certain aspects of the environment. However, adverse environmental and sociological impacts have been identified during and after many reservoir constructions. Whether reservoir projects are ultimately beneficial or detrimental to either the environment or surrounding human populations has been debated since the 1960s and likely before then, as well. In 1960 the construction of Llyn Celyn and the flooding of Capel Celyn provoked political upr