Regulation of nonpoint source pollution often relies in one way or another on policy instruments based on ambient indicators. For well-known reasons, enforcement of ambient-based policies is, at best, limited. If no individual choices or actions are observed, than ambient-based regulation might...

When a nonpoint source pollution process involves many polluters, each taking his own contribution to aggregate pollution to be negligible, ambient-based policies become ineffective due to lack of strategic interactions between dischargers. We offer a regulation mechanism for this case. The...