What does the NPDES prohibit regarding water pollution?

The National Pollutant Discharge Elimination System (NPDES) primarily focuses on regulating the discharge of pollutants into the waters of the United States. The correct answer indicates that the NPDES prohibits the unregulated, or unauthorized, discharge of pollutants into surface waters, which is essential for protecting water quality and public health.

By requiring permits for discharges, the NPDES establishes a framework for managing the amount and type of pollutants that can enter U.S. waters, thereby aiming to maintain the integrity of aquatic ecosystems. This permits system ensures that any wastewater discharged meets specific regulatory standards designed to reduce harmful impacts on water bodies.

The other options relate to aspects of water quality management but do not accurately capture the core prohibition established by the NPDES. Non-permitted discharges of chemicals, while relevant, fall under the broader scope of the prohibition on pollutant discharge. Water quality assessments by states and the discharge of treated wastewater are activities that pertain to water management strategies but are not fundamentally what the NPDES prohibits. The focus of the NPDES is specifically on ensuring that no pollutants are discharged without appropriate oversight and regulation.