For federal agencies, preparing an EIS is primarily to ensure compliance with which act?

The primary purpose of preparing an Environmental Impact Statement (EIS) for federal agencies is to ensure compliance with the National Environmental Policy Act (NEPA). NEPA mandates that federal agencies assess the environmental effects of their proposed actions before making decisions. This includes evaluating the potential environmental impacts, considering alternatives, and engaging the public in the decision-making process.

By preparing an EIS, agencies provide transparency and accountability regarding their actions' environmental consequences, fulfilling NEPA's requirements to inform both the decision-makers and the public about possible environmental effects. This process helps in promoting informed decision-making that balances environmental protection with project development needs.

While the Clean Water Act, Endangered Species Act, and Wilderness Act are also important environmental laws, they serve different purposes and do not specifically require the preparation of an EIS. Each of those acts has its requirements and focuses on particular aspects of environmental protection, but NEPA is the overarching framework that necessitates a formal EIS process for federal actions that significantly affect the environment.