Which agency was empowered by the Clean Water Act of 1972?

The Clean Water Act of 1972 was established to regulate the discharge of pollutants into the waters of the United States and to ensure water quality standards. The Environmental Protection Agency (EPA) is the primary federal agency tasked with enforcing this act. The EPA has the authority to set water quality standards, oversee the permitting process for discharges, and enforce regulations to protect water resources.

The other agencies listed—such as the United States Department of Agriculture, Bureau of Land Management, and United States Forest Service—focus on different aspects of land management, agricultural policies, and public lands, but they do not have the specific mandate to regulate water quality at the federal level as the EPA does. The EPA's role is crucial in implementing the provisions of the Clean Water Act, making it the correct answer in this context.