What best describes the Clean Water Act's approach to pollution?

The Clean Water Act primarily aims to restore and maintain the integrity of the nation's waters by regulating discharges of pollutants into them. This approach involves setting water quality standards and requires permits for the discharge of pollutants, ensuring that any release into waterways is controlled and monitored. The Act focuses on the management of water pollution through a framework that includes both federal and state oversight, effectively balancing economic and environmental interests.

The other options introduce concepts that do not encapsulate the core intent of the Clean Water Act. While self-regulation and penalties are aspects of environmental compliance, they are not the central focus of the Act itself. The notion of unlimited modifications to waterways contradicts the protective measures inherent in the legislation, which seeks to limit and manage alterations to preserve water quality and aquatic ecosystems.