 Planning had begun for the project in the 1960s, when the agency began acquiring properties that had to be vacated prior to flooding of a large area subject to inundation.The National Environmental Protection Act (NEPA) of 1970 provided for agencies to assess the environmental effects of their projects prior to undertaking them.Opponents of the dam project, who were concerned about its effects on the habitat of the valley, filed suit for an environmental impact assessment to be done, although the project was already underway when NEPA was passed.